It's partly for the feel, and partly for the texture, and partly for the way it won't "bubble up" if you move your mouse quickly across the surface with pressure. At least, that's my reasoning. My desktop works, but I want something that is a separate entity and can be cleaned easier.
Looks have a bit to do with it, as well. I can go for any of the pads I have listed. Each has its strong points. I figured I would toss it out there and let the members give me some feedback. I was hoping for some who have or have had these pads.