Several weeks ago I replaced a 2000 mile tire. The repacement (not sure of brand) was defective and the bead seperated after about 100 miles. The mech at the LBS offered to upgrade me to a "Specialized" if I'd pay the difference. The bad tire had a fancy tread pattern and colored sidewalls. The new an substantially more expensive tire was plain black, except for an obvious logo and had no tread at all.

In response to a question about the lack of tread the LBS owner allowed, "You may notice slightly less traction when riding hard on wet plate glass surfaces. Otherwise the tread makes no difference."

Since I live and ride in a desert, most of the plate glass roadways are usually dry. Thus I have noticed no difference at all.