I blame Vista for this... and before you start egging me, let me explain...
While Vista was/is a steaming pile of crap for many reasons, in a lot of respects it was hardened against malware, to a better extent than XP was.
Because Vista WAS such a steaming pile of tripe, people held onto their XP boxes much longer, and thus gave a greater pool of boxes to infect with the plague.
Now that Win 7 has come out, and actually looks like it has legs, hopefully we will start seeing all the older XP boxes start to get replaced, and a slight drop in the pool of pwned machines.
I know I am dreaming, but its nicer in my dream world, now I will go back to getting my massage from Keria Knightley, and Kate Moss.
Mines the one with the Win 7 RC 1 DVD in the pocket...