As always Sheldon has the answer.
http://sheldonbrown.com/tyres.html
thanks, good info:
'Tread for on-road use
Bicycle tyres for on-road use have no need of any sort of tread features; in fact, the best road tyres are perfectly smooth, with no tread at all!
Unfortunately, most people assume that a smooth tyre will be slippery, so this type of tyre is difficult to sell to unsophisticated cyclists. Most tyre makers cater to this by putting a very fine pattern on their tyres, mainly for cosmetic and marketing reasons. If you examine a section of asphalt or concrete, you'll see that the texture of the road itself is much "knobbier" than the tread features of a good-quality road tyre. Since the tyre is flexible, even a slick tyre deforms as it comes into contact with the pavement, acquiring the shape of the pavement texture, only while in contact with the road.
People ask, "But don't slick tyres get slippery on wet roads, or worse yet, wet metal features such as expansion joints, paint stripes, or railroad tracks?" The answer is, yes, they do. So do tyres with tread. All tyres are slippery in these conditions. Tread features make no improvement in this.'
i won't be commuting with my pro 4s, just for winter runs to stay in shape