Because we use Change Management. And when we started with it in 10.0 it would only go from one state to one other state. It will go from Under Review to Production Released but then you can't go from Under Review to Prototype Released or Pilot Released. So we had to have the other two XXX Review states.
I understand that in 10.1 or maybe 10.2 it allows you to go to one of three (?) states? But went we started we couldn't.