This report is a bit of a surprise - and a wonderful opportunity.

Cool report.

I totally believe this. If you look at the hsc Common Workspace Server you'll see the top domains reported by Purify users are all US! geocities, yahoo, aol, and verizon topping the list.

As far as I can recall, the US is always at the top of Spamhaus' list:
http://www.spamhaus.org/statistics/countries.lasso

It would be interesting to see not only where the spam is coming from, but where the money is going in the end.
Spam routed from a certain country may be the work of spam gangs in a different country.