SD DVD is nowhere near 720p
First off 720p is 1280x720
Standard DVD is 540x276
Progessive scan DVD is 640x480
640x860<1280x720...
on Blu-ray's the good thing is that it supports actual seamless branching unlike HDDuD, so they can include the Extended/directors etc on the same disc and you can choose it using seamless branching. BD's Seamless branching is better than HDDuD's seamless branching
Seamless Branching FTW!!