They do have a point though
A wireless mouse will require batteries. If you're on the road, there's nothing more troublesome than having a nice wireless mouse that you can't use because you ran out of batteries.
I checked out their website and i'm not so sure that the 'wire monster' (aka: a conventional mouse) is a reason why i would want to buy their slim-mouse though. I found that if you roll up the cable nicely enough, you won't find the monster :) So it's basically for people who don't like to wind up the cord? Well then, those people will be in for a surprise to learn that they still have to do that. Albeit a bit more delicately than with a conventional mouse.