It think it's a simple case of volume. I live in Philadelphia, now of course we have some "tourist" restaurants like Ruth Chris which is on Broad street next to our theater. sure if you want to eat there at a specific time reservations are definitely suggested but face in, there are a gazillion restaurants in Center City, so it is virtually impossible to NOT be able to sit down some where.
South Philadelphia is an Italian restaurant heaven, you darn near can't walk 2 blocks without passing 5 really good Italian restaurant. that's one reason whey people love living in big cities. I can walk out my door in Fairmount and have no issues finding good food with minimal wait.
If you are in Philadelphia or NYC and you wait 1 hour to get a pizza some thing is seriously wrong. there are simply too many pizza joints for you to ever have to wait.
Same thing with Paris, yes if you want to eat at the top of the Eiffel Tower you will need reservations. If you want an great meal chances are you can walk to one of the Bistros or Brassieres and get an excellent meal. My entire family went to Paris (8 people) in 2013 during May (high season) we did not make i reservation, we did not have any issue with finding a great place to have dinner.
so I do research a vacation destination but I have never, ever in my life have to make reservations to eat 6 months out.
London, no
Paris, no
Washington DC no
Vegas.


if you stay on the strip every hotel has about 7 restaurants inside. you don't even have to go outside to get a meal at the last minute and all you have to do to get booze is sit down at a slot machine.
Paris about the only thing you have to do is buy a museum pass and check opening times. after that you will have no problem