Yes it's probably the Fcheck that **** things up. I installed a maya .iff plugin for PS and it was ofcoures 720p.
If I render out a shot from your Maya file the images are 1280x720. There is nothing wrong with the images coming out of Maya.
Hit render save the image and open it in something other than fcheck, you should see the image is 1280x720. Not sure what's going on with your fcheck I never use it.