This is actually quite common in recent years for bug hunters and exploit developers. I can think of a dozen or so companies that do the same thing. Immunity is another example.
Trying to use a moral argument to get out of compensating someone when you have the resources to do so is shameful. Sorry, but this stuff is worth far more than the (up to) $3133 they are offering.
No More Free Bugs, as they say.
They can either pay a nominal fee for doing their security work for them, or they can hire some equally talented people and fund this type of research on their own internally. Fair is fair. There is no reason this isn't worth compensating but something like pagerank optimizations is.