I don't think it's surprising either, nor will I be surprised if the birth rates of the Muslims, Mormons, and evangelicals fall, along with massive apostasy from those religions. It was kind of a dumb prediction, because in Will Durant's time, it was a cliche that the young generation was much different from the old generation. The birth rate had already fallen considerably, and Catholics are hardly isolated from the larger society. But - what about the men in black hats? The Amish, the Chassidim, the Hutterites, the FLDS, maybe the Mennonites. I don't have time to do a lot of research right now, but I think these groups have somewhere between 1/2-1 million members between them. All of them have high birth rates and low out-conversion rates. When the times are a-changin', these groups are completely impervious to that change because they have little contact with the outside world. In fact, change just makes them more alienated from the outside world as it becomes more alien to them. These groups thrive while other religious groups tend to lose members or become liberalized. If modernism was an antibiotic, these groups would be multi drug resistant organisms. I don't feel confident about making predictions about the future, but if there's one thing I will dare to predict, it's that men in black hats will continue to have big families absent a Malthusian check, persecution, etc. At a doubling rate of 25 years, the 1/2 million estimate gives them 250 years until there are about 500 million of them. I don't really believe that will happen, but the interesting thing is that if it doesn't happen, that will mean that something bad has happened to them, or else that they decide to reverse centuries of tradition for reasons that are completely unfathomable now.

Losing surplus boys isn't going to affect the growth of polygamists. Women are the bottleneck, not men. If you got rid of 3/4 of the men while marrying off all of the women, the population would be 5/8 what it would have been with the men, and will grow just as quickly. 5/8 * 2^10 * current population is a pretty big number. I don't know much about the Mennonites, but low Chasidic retention rates contradicts what I've read. I can't find any real data, but a brief search finds lots of references to their high retention rate (uncited in blog posts, newspaper articles & the like). Maybe you're thinking of Orthodox Jews, who do have a relatively low retention rate? Mormons are kind of a wild card. They have high birth rates but also high apostasy rates: http://religionnewsblog.blogspot.com/2008/02/religious-retention-and-apostasy-in.html It's hard to say what will happen to them in the future. I doubt their missions will do much good, because their religion is blatantly stupid. Who in 2010 would convert to Mormonism after googling "mormonism" for any reason other than the desire to marry a Mormon or get ahead in a Mormon community? Sure enough, Mormon conversions are down since the internet became ubiquitous: http://www.rickross.com/reference/mormon/mormon254.html My hunch is that their birth rates will drop and their apostasy rates will go up in the short-moderate term future, sort of like what already happened to the Catholics. They're not detached enough from the larger society to not feel its effects.

Mark, just out of curiousity, how do you plan to make your four kids?

Hitler was extremely cocky. He expected the West to stand aside as he conquered the East, and Russia to lay down and die as soon as it was invaded. He was wrong, but the idea was not totally crazy if you look at their past behavior. 
 
As for his plans, I think he intended to do something in between England's colonization of India as an elite minority and the Anglo-Saxon colonization of North America through genocide. This might just be because there simply weren't enough Germans to plausibly colonize all of Russia, so there would be nothing to gain from exterminating them all right away. 
 
Here's a quote from his Table Talk that sheds some light on his plans for Russia: 
 
The German colonist ought to live on handsome, spacious  
farms. The German services will be lodged in marvellous  
buildings, the governors in palaces. Beneath the shelter of the  
administrative services, we shall gradually organise all that is  
indispensable to the maintenance of a certain standard of  
living. Around the city, to a depth of thirty to forty kilometres,  
we shall have a belt of handsome villages connected by the best  
roads. What exists beyond that will be another world, in which  
we mean to let the Russians live as they like. It is merely  
necessary that we should rule them. In the event of a revolu-  
tion, we shall only have to drop a few bombs on their cities, and  
the affair will be liquidated. Once a year we shall lead a troop  
of Kirghizes through the capital of the Reich, in order to strike  
their imaginations with the size of our monuments.

OT, but some of older posts are showing up as raw HTML in my browser (Firefox): http://www.gnxp.com/oldblog/nopub/85379116

I don't have time to look this up right now, but I wonder if this is influencing the popularity of sex-selective abortion. Are young couples looking at these hopeless bachelors and deciding that maybe having a girl isn't so bad after all? Or does dad optimistically think that his super-studly DNA will guarantee that it won't happen to his son?

Looking at the numbers on the Y-axes on your graphs for whites/Asians and NAMs, I'd say there's plenty to worry about. Teen pregnancy is the least of it. 
 
As for teen pregnancy, it seems that it should go up eventually because the quickest way a woman can reproduce her genes is to get pregnant as a teen. If you were a woman who wanted to reproduce your genes, what would you do? Crank out as many babies as possible with the highest quality men you could find (in practice this would probably mean alphas). The state will take care of them if you can't, and if you are going to do it yourself, better you should do it when your mom is still young enough to help (also better that you should be 30 and not 50 when your little treasure starts cranking out her own bastards). 
 
I don't have time to try to confirm or refute this right now - if I did I would try to find out if women who start young have above-average reproduction rates. Maybe tomorrow. But I strongly suspect that they do, that not all of them are going to be susceptible to the harmful (from an evolutionary point of view) trend against teen pregnancy, and that those who aren't susceptible will tend to increase as long as the strategy is viable.