I think Schneier is one of the most intelligent voices in the debate on terrorism but I'm not convinced you sum up his position entirely accurately. I had a browse around his site to see if I could find some specific data to confirm your claim and had trouble finding anything. The best I could find was Portrait of the Modern Terrorist as an Idiot but it doesn't contain actual data. I'm rather confused why you linked to the specific blog post you chose which seems largely unrelated to your claim. Do you have any better links you could share?

Note that in the article I link he states:

There is a real threat of terrorism. And while I'm all in favor of the terrorists' continuing incompetence, I know that some will prove more capable.