BUT (and this is big one) in many instances, such as Google and Facebook, you do have to be brilliant to get in.
That puzzles me. Why would one want to get into Facebook? Do they pay that well?
They build some amazing technology. I don't think I could get over my issues with Facebook enough to work there, but part of me desperately wants to work on Hack and HHVM with them (thank the flying spaghetti monster for open source software!).
It's all open source. Here's HHVM: https://github.com/facebook/hhvm. What's stopping you from working on it now? For all intents and purposes you would be hacking on it with them.