I don’t think its possible to prevent people from submitting a URL with the info required when submitting a comment. But, thats how the spammers are coping now. They know we block URLs inside comments, so now, they just put them in the information that WordPress requests before allowing a comment to the next stage.
I don’t get a massive amount of spam, but what I do get annoys the crap outta me. so… given that I get 90% spam and 10% genuine (or none), I’m actually going to insist that, for a while, if you want to comment, you need to be registered and logged in. Since most of the spam comments are likely submitted by bots, this *might* get round the problem. Unless the bots can bypass the registration. We shall see how it goes.
Its getting awfully tiresome.