I don't think tires are made with mold release anymore, but they still have a slick surface from the mold - and may have a coating for storage, as well. Try to get a tire maker to 'fess up on this one, though.
UPDATE: I did some searching around, and found that mold release is still used, but it's not the old greasy stuff from days gone by. Many makers of it advertise how their stuff stays on the mold, and may be used for a day's production without reapplication, implying not much sticks to the tire, if any. Modern molds are more highly polished than years ago, too, which may be why the tires don't grip until worn a bit, but 100 miles may be more than needed. The exception is when the tires come with that grayish-white gunk on them (which I've only seen on auto tires, so far); I think that keeps the surface from ageing in storage, but I haven't found any comments on it, except it is nasty looking.