Why big companies pay better
I’m not particularly surprised that big companies pay more than small companies. It stands to reason, really: successful companies will (a) be able to pay more than unsuccessful companies; and (b) be much more likely to grow to a large size.
The advantages of working for a small company don’t come in your regular paycheck. Instead, there’s more option value, if you’re at a start-up: the small but valuable chance that the company will be a huge success. Plus there’s often more collegiality and less bureaucracy, and any one individual has a much greater chance of being able to make visible change happen. But if you mainly want to maximize your take-home pay, working for the man has a lot to be said for it.