Did the bluray version come with an extra DVD?
There may be an Avatar released for the newer 3D version. But as shrewd as movie companies are in the business, I tend to believe that releasing the movie exclusively in newer 3D would enrage the majority of paying consumers. There is only a niche market initially who would pay for a brand new flat panel just to be able to test and watch Avatar in the new version in 3D. They certainly wouldn't ignore the hundreds of millions in income that can potentially be generated from those hesitant to jump in on the new technology just for one disc.
For the old audience, there's the 2D version. Unless, they would create three versions, so you have to triple dip. Although having two 3D version would make it confusing on the retailer/consumer. Most big studios have refrained from releasing old 3D version of 3D movies. Disney didn't release 3D version of Toy Story 1&2, Bolt, etc. Dreamworks has not released Monster VS Aliens in 3D. Only lesser releases from studios like Coraline, My Bloody Valentine, Final Destination...
3D is the next big thing, especially in the US. They want to have something for the early adopters. And with the economy especially picking up, consumer spending is on the way up as well. So studios and tech makers are hoping 3D will be a big reason to upgrade, and what better film to showcase than the biggest moneymaker of all time...
We are a bit off topic na...
In the US, it's DVD+Bluray combo. Highly unlikely here as all DVD+Bluray Combo becomes separate releases here especially Disney, though that's a different studio...