It's BS. My guess is that the 3D conversions are all underway and some aside from TPM may already be done. They're just saying that so enough people think, "Well, if I don't see the prequels in 3D then I won't see the original trilogy in 3D, so I have to make sure to see the prequels."

Lucas has been doing this for 15+ years. 1995 - final home video release. 1997 - special edition only in theaters. Get my drift? It's called MARKETING.

Even if not all the movies are released in theaters, they will be released on 3D blu-ray.

Profits from 3D theatrical release and eventual blu-ray double dip will help finance a new trilogy ("episodes 7,8,9"). That's always been my theory. Lucas will produce but hire another director.