That's because generally speaking, Coke in a restaurant is more towards the sweet side (still not as horrifically sweet as Pepsi). Coke from a can (or a plastic bottle) has a highly acidic finish, whereas Coke from a bottle has a smoother finish. Pepsi from anything is just plain nasty. :-P Diet anything is worse.

OK, that, and Pepsi is far less widely available in restaurants.

I am the Doctor, and THIS... is my SPOON!