I have a theory so I want to run it by a couple of folks first.
The thing that people forget around here is the primaries are are just 1/2 the battle. The behind the scenes stuff is the other half. Despite the words of some that they no longer exists, the smoke filled rooms of yesterday are still around, they just have been replaced with catering and laptops, but the maneuvers are the same as the have been for 200+ years.
I have expected the GOP to be a little more surprised at McCain's rise than they have indicated. It is like they expected it. I also know the powers that be have no interest in taking him into the general, or at least need an escape plan.
McCain has openly gone against the GOP by joining the Gang of Fourteen and in various other ways. Unless those in control of the RNC are actually enemies of the GOP (which is possible) I would think they wouldn't want McCain to take the nomination.