That would explain things. Have the Bitcoin devs fixed the timewarp (sorry for lack of a better description, that's the only word I could think of) issue and what's there to stop someone from doing it right now? Or is there still a bit of muscle required to overcome the existing 10-12TH/s on the network?
1. No.
2. You still roughly need 51% to do it, so something like 15Th/s for bitcoin...