Nobody knows quite what happened or why, but I think that it will be concluded that aggressive deregulation was a major contributor.  
 
My superficial impression is that the US, GB and Spain all had property valuation bubbles, but the Spanish generated less bad paper and less damage to the banking system. I don't know if this is due to better regulation or failure to takke advantage of the wonderful free market. 
 
The empirical test might be to compare a country which had a housing bubble but didn't lever up bad mortgages and hand the proceeds to executives. I expect you'd find some institutions in deep trouble, but not the wholesale implosion of the financial sector that we've witnessed. An appropriate example might be Spain. 
 
For what it's worth, Australia had/has a housing bubble but is apparently* one of the few OECD nations that's still tracking (barely) to avoid a recession. (As of Dec 15, rates of 1.75% for 2008-9 and 2.5% for 2009-10 were forecast**)  
 
The Labor government is saying that this is due to the relatively stringent regulatory structure here, and I'm not aware of any local commentators trying to argue the contrary.  
 
*www.abc.net.au/news/stories/2008/11/26/2429657.htm 
**www.bloomberg.com/apps/news?pid=20601081&sid=aB_M7zBVQDCo