The difference between 720p and PAL is about the difference between PAL and VGA.
720p and 1080i actually need about the same bit rate.
720p on a 1080 line screen is degraded compared with 720p on 720lines
1080i or p is degraded on 720p screen
Everything is degraded on 768 line (commonest HD screen).
SD (576) is degraded (progressively less) on 720, 768 or 1080 line screens.
HD should be 1152 line in Europe to give a significant improvement on 60" screens an ensure no degradation of SD.
Instead we are going to be offered 720p because too many TV sets can't do 1080i properly and instead of the better compromise 1080 which does not degrade SD so much.
1080 is derived from visible lines of old Analogue 1125 line for Japan (thus NTSC derived). VGA is of course progressive version of visible lines of 525i NTSC.
The US & Japan have messed up PCs and now HDTV for us :(
Anyway... there is nothing decent to watch anymore. When the format war for HD is over and penetration is 30%, I'll buy a HD projector and player for Cinematic titles. Till then I'll stick to previewing HD in the office and my 21" 1600x 1200 PC with Satellite Card. And buying regular DVDs for the telly,