I've had something similar happen to me at Chefs de France - I got there 5 minutes early for my reservation but had a 35 minute wait. That coupled with a rude maitre d' meant that I ended up asking for my desert to be comped (which to their credit, they did). I understand that they have space restrictions and I don't mind a short wait, but given you have to give a credit card to confirm a reservation for a set time, they should honour the same.
OP - you are remarkably chill about it. I agree with some of the other posters who point out that this isn't usual (and out of my last 4 trips, it's only happened to me once) but if it happens, there should be service recovery to recognise that you're being put out.
1F