I don't know of any reports on it, but from personal experience, the amount of time spent on average per physical server I configure and shift around is a tiny fraction of the time I spend dealing with AWS peculiarities you don't have to deal when you control your own hardware (I currently split my time 60/40 between two clients - one with a physical hosting environment set up as a private cloud split over two colo's, and one in AWS)

The company I manage physical servers for would go bankrupt if we were to pay AWS level rates. Last time we priced it out we were looking at ~3x hosting cost - including fully loaded cost for staff time spent on maintenance etc.