So is it Directv's plan to only do 1080p over DOD (internet)? Or possibly via satellite as well?
Internet ONLY. There isn't enough sat bandwidth for it, at the bitrates they are using for DoD, without reducing channels.
As downloading HD movies becomes more common, bandwidth issues and download caps ARE going to be a problem for most people, which is why it will be a long time before disc-based media (i.e., Blu-Ray) will be replaced by downloads, though downloads will likely be the primary method eventually (a decade or more). In 2 years, you'll be able to fit 64GB on a MicroSD card, but it will probably be 4 years before they'll be cheap enough ($5 or so) to make them the format of choice.