What’s It Like to Work at Google?

Average companies generally don't have the resources/incentive to hire the best, so they don't need to provide the same perks. They're also less likely to invest their time speculatively, so no 20% time.

I'm sure there's a happy medium where the right amount of perks and fun culture improves company productivity more than it costs up front, much like decreased taxation can sometimes increase tax revenue. I don't think many companies feel confident enough to determine the line appropriately, and I imagine it's more comfortable as a manager to err on the conservative side.