Many people infected?
Erm... PCs actually, and only Uncle Bill's rat-infested OS at that.
And what happens when Windows is replaced by Linux/MacOS...yes all those virus/malware writers out thre will attack that OS. The only reason Windows is targeted is because it is the most popular, computer viruses are just like biological viruses and exist ONLY if there is a viable host.
Mark, you pretty much hit the nail on the head. If ISP's filter this crap out (and we know they can, they jus choose not to) then a lot of botnets used for spam/DOS/DDOS will die off. Inline malware would be cut down a lot as well, you won't get 100% of this stuff 100% of the time but it would be a big help. Hell, it would also make the internet go faser too! Imagine, an internet that isn't clogged with spam and malware....utopia.
There is some light at the end of the tunnel though, most anti virus systems now do NOT ask you to update, they just do it. And it's about bloody time too!