Well, Bubblecup didn't really make Hasbro any more money than an art pony would have. They ALWAYS sell out all of their SDCC ponies very soon after the con, and they always are produced in limited numbers. Remember, these are ponies that Hasbro themselves must haul to San Diego--along with Transformers, Jem, etc exclusives. They have a limited amount of room.
Whether 500 people line up at their booth or 5 million, they will probably have about the same amount of ponies available.
SDCC ponies aren't really produced to make money, unlike a pony sitting in a toy store. Hasbro is paying a lot of money just to get a booth at the convention.