They actually do pay shitload of money to senior and especially principal people, mostly in the form of stock grants. They have really strange vesting schedule too: something like 5% first year, 5% second, 45% third, 45% fourth. To compensate for the dropped income they give you sign-up bonus for first and second years.

I left before my first vest as soon as interesting start up showed up (start up didn't survive, but at least it was fun).