Then how does 720p work in Virtuous and sense based roms?
For exactly the reason that they
are Sense based Froyo ROMS.
Virtuous is a Stock HTC ROM with the bloatware removed and a few goodies added. The other Sense based Froyo ROM's all use HTC's Sense framework where the Video Driver was mostly, if not completely, done before they started working on their version of the ROM.
CM6.1, though not Sense based, is Froyo and the devs were able to hack the Video Driver to get it to work. The difference between Froyo and Gingerbread is like Apples and Oranges, it's a completely different driver type and the hack they used in 6.1 will not work.
CM7 will most likely get 720P Video eventually, but not any time soon. However, as it stands now, it's not happening until they can get their hands on a leaked RUU.
Remember the first rule of CM…. No ETA’s!
I hope this helps you understand that the CM devs are not “dissing” the DInc. It’s a function of Time vs. Functionality. They could spend months coding a new video driver (no small task by any stretch of the imagination), or they could put that same time into developing new features elsewhere. The Video driver will come eventually.
If my answer is coming off as snarky, it’s not meant to. I’m just trying to explain why it’s not there yet and won’t be there in the near future as clearly as I can.