Probably no longer fair to say that all riders are on tubulars...it would be an interesting stat to see. Last year for sure there were a few on clinchers...there is a photo of someone rolling a clincher off a rim in a sprint. I believe there are a few on the new tubeless tires.

It would be fair to say the majority of riders are on tubulars though and they are probably all on 21mm wide or there abouts tires. Maybe 19 mm for time trials.