I'm surprised at the number of bike mechanical issues that I see in the TDF television coverage. There are 9 riders on each team and they ride roughly 5 hours per day. That leaves 19 hours per day to do bike maintenance and each team has a couple of mechanics.
The most common thing that I see is rear brake centering issues. For some reason, I haven't seen them fiddling with front brakes. The second most common thing that I've seen is rear derailleur limit screw adjustments (while leaning out of a car at around 25 MPH).
There's obviously something that I'm missing because I'd be embarassed if I only had to maintain 9 bicycles and they still required on-the-road adjustments.