It was clearly a legitimate interception.
Replay during regular season is generally good. Replay during the playoffs is sometimes atrocious.
If a hot buzz team is in danger of losing, and missing the NFL's biggest day, the corporation will sometimes take action. That was the reason for this reversal. NFL has a long history of that in playoff games.
It's a business, guys. As another poster pointed out, without darling Indy in Detroit, the SB will be cold indeed. All the hack writers and flacks who labor at NFL will really have to squeze it to get some juice from the buzzless teams that will be in the SB.
Nice try, NFL. But not this time.