I think innovation starts with policies and leadership that allow for it.

Big companies get process heavy and often simply wouldn't allow it to occur anyway.

"We're going to be super innovative, now go get 8 non technical manager's approval!" It doesn't matter how innovative your people are at that point. Sometimes it's just the volume of people in the mix who can hold things up... big companies just have more opportunity for people to stifle innovation even if just out of misunderstanding, ignorance, etc.