I can't blame WWE or Rock. WWE isn't going to pay someone premium dollars for 3 or 4 appearances a year and Rock has bigger fish to fry with his movie career. I think if anything, WWE should leave the door open if Rock wanted to make appearances, but leave it on a pay-by-appearance basis, not a formal contract.
January 4th 1999 - The day WCW injected itself with 10 gallons of Liquid Anthrax...AKA...The day Hogan "Defeated" Nash to win the WCW title in front of 40,000.
My opinion? I think they should have at least kept him on a retainer and then, as dskillz points out, pay him on a per-appearance basis going forward.
I wouldn't do this as anti-competitive measure (I mean, even IF he ended up on a TNA or Japan show down the road, who cares?), but more as a show of good faith. This way, if he wants to show up at Raw one time to plug his movie, or even wrestle a match, you don't to have start negotiations from scratch and worry about any possible bad blood between the two parties.
In fact, I think they should do that with a handful of other guys, too -- maybe Austin, Foley and Hogan. Again, just as a show of good faith.