Just that. They've gone back to the original film elements, redone the effects and made TNG look great at 1080p resolution, with audio to match...
But the thing is that the original TNG releases were much lower than DVD tech, little more than VHS resolution, video composited effects work, and with soft, ghosting imagery. Whereas most feature film DVDs can be upscaled to hi-def TVs with resasonable results, the same can't be said for late eighties NTSC television.
If the new masters of TNG were put onto DVD, they'd be able to get the max out of the 480 line resolution (576 for PAL) and would look as good as they'd possibly could, and would be a useful alternative for those not yet on the Blu bandwagon.
After all, the remastered TOS episodes got a DVD release as well.