Yes, they can't put you in a VIP room and don't bring champagne, but treats in the form of bonuses and special offers are even better if you ask me.
They'd probably receive the same rewards (or maybe better) since there are different ways on how rewards can be calculated and afaik house edge is higher on physical casinos.
Maybe, if casino owners knew. My point is that as far as I've always seen it, in physical casinos, you are considered are "VIP customer" just when the management and staff already recognize you (same as if you come to a certain restaurant often, you can get discounts, because the owners already know you), but this can be tracked way better in online casinos. There are certain rules: e.g. make 10 bets worth 10$ each and get X free spins. After a year of being registered - you also get certain bonuses, same goes with holidays, your b-day. I just can't see how this could work with offline casinos. The max you can get is maybe some sort of client's card, so they can track how many times have you visited them, but other ways of recognizing client are complicated.