Bear in mind that the professionals both have the opportunity to change
bikes if something goes wrong and probably don't use the tyres they ride
in a race like P-R much more than once.
It would be interesting to compare how often someone like you who rides almost every day on cobbles gets flats and has to change their tyres compared
to someone riding on normal roads.
Unrelated... I have done several long events on cobbles and never had a puncture.
I'd imagine the combination of lower pressure and frequent bumps would
make the chances of snake bite punctures higher. I ride quite a bit on cobbled roads here in Flemish Brabant, but I couldn't say if I wear out tyres or get flats more often.
I do know riding on cobbles is hard on other components, particularly for
inexperienced riders who try and change gear at speed on cobbles. Seen more than my share of mangled mechs. A lot of riders use a little device to stop the chain jumoing off the small ring and Tom Boonen apparently has his rear mech adjusted so he can't shift into the biggest sprocket, to prevent his chain jumping into the spokes.
So maybe these things are more important than tyre problems on cobbles...