i like it wet...

[yudalicious]

tires that are designed for wet surfaces have more grooves cut into it to channel the water out of the path of the tire, and yes tires designed specifically for the wet do have less grip in the dry than some tires due to the fact that they dont have as much surface/contact patch.

tires designed for the wet do have less grip, although I'd say the reason is more due to tire compound than surface area. ie: take the tire compound of an all season and turn it into a slick, it's still not that grippy. Generally, a grippy tire in the dry is still going to be grippy on wet pavement without standing water.

edit: although this is talking about race tires, it's pretty spot on:
http://en.wikipedia.org/wiki/Rain_tire

As you can read the grooves really only channel the water out of the way as a main function, although I wanna say that a reduction in surface area and a concomitant increase in pressure (pressure = force/surface area) help grip in the wet/snow as well.