In nearly any casino, the average play will be weaker than what it is online. The main reason behind that is online poker (at least partially so) is played at specific software, which is designed to provide the opportunity to play POKER.
(which is also the reason why many people look for online gambling sites, which simulate not only poker, but tons of different gambling games - roulette
- you name it) many people come to play just for fun / take a shot at poker / blow off some steam from a big loss at a roulette table - in other words, many different reasons, which indicate that they are not at a casino to grind.
There is a great scene in "Rounders" which nicely explains that the regs at casinos usually wait / specifically look for tables that have these random gamblers.