As you say I doubt many spammers would get into the 100 edit a month league before being blocked.
Of course a lot of rollbackers will be in the stats, and if there had been a drop in spam then some of the spam fighters might drop below 100 edits a month. But since the big announcement today about a 350 account sockfarm that had been spamming Wikipedia, I think it would be odd if spam overall was down on the year (I seem to remember some research a few years back that showed spam steadily rising year on year)..
My experience of spammers who create articles is that once their article is deleted they are often left with fewer than five live edits, so unlike vandals many of the spammers will not make the 5 edit a month figures.