I find this a bit shocking because 3D releases of the previous films could only hype the release of the new film. But on the other hand, it would have to be the original trilogy being re-releases since the new Episode VII is a sequel to those.
Here's the official statement...
Lucasfilm has decided to postpone this fall's scheduled release of Star Wars Episodes II and III in 3D. Given the recent development that we are moving forward with a new Star Wars trilogy, we will now focus 100 percent of our efforts on Star Wars: Episode VII in order to ensure the best possible experience for our fans. We will post further information about our 3D release plans at a later date.Source: Star Wars.com