That would certainly reduce them. However I have seen a lot of blogs where if you put your link in the name/email/url field its ****************, but if you put a link in the comment its nofollow, or vice versa. So that would still throw it off. Plus the blog admin can, of course, can respond to someones comment and put a link in that would be nofollow, even if it typically was a **************** blog.
Secondly, people use sbox for more then blogs. I know I use it to check PR of all kinds of pages, and use it to filter/merge and manipulate all kinds of things. So people would natually want to use the **************** checker on more then just blogs, on all manner of sites, at which point they would request/complain/ask for support if it didn't work on all sites..... The only way it would really work is if you had a decaptcha type service where you had people checking by hand.
huh, maybe I should start that service..... ToFollowOrNotToFollow.com...

Anyone know who runs decaptcha? I could get in with them... lol
Good thoughts though mate.