I trust that you're not going to complain if they quit your project for a project that does offer them equity.<p>FWIW, no one is indespensible in a startup; some are merely harder to replace than others. I'll bet that "original idea" guys are getting equity even though they cease to be indespensible.
I'd list such people under "suckers". YC doesn't provide enough money to pay anyone a decent salary, so anyone who isn't getting equity is being short-changed.