Oh, yeah, I didn't notice that in his post, the BD will be 720p of course - same video track as the mkv. There is a certain amount of fine detail lost of course but considering that the resolution is about half (921600 pixels for a 720p frame and 2073600 pixels for a 1080p frame) the amount of detail lost is quite small - it has to be for the reasons mentioned by Stinky-Dinkins. It also helps the other sources blend better, since in 720p their resolution is met half way with that of the BD.