Pretty much all counters require that some script is put on your page. My bot scans for scripts and things, and directly rejects anything with a script on the page.
So your counter wouldn't have as much to count, I guess.
Decent server side stats are pretty easy to get set up, awstats and others will give you pretty much the same information as the counters (and this is why you don't see the counter people around much pushing their product because they know they are in a mature market now).
Alex