Source: The Wrestling Observer
Vince McMahon's hip problems are said to be legitimate. WWE had Brock Lesnar F5 McMahon at the end of RAW and then ran with the storyline that the chairman suffered a broken pelvis. The storyline was so that Vince could be written off of TV and get the surgery that he needs.
The change also allows Triple H to return as McMahon's replacement, which can then kickstart his renewed feud with Brock Lesnar leading into WrestleMania 29.