This debate will go on forever. The only way to judge the quality of 1080i vs. 720p is with a reference-grade DTV monitor, such as Sony's $30,000 BVM-D32E1WU. This monitor has a dot pitch of about .3mm, which is extremely fine.
The quality of film transfers, the data compression, and quality of MPEG-II encoding and decoding are all factors which determine the final quality of a 1080i or 720p image.
I have watched "The Practice" and "Alias" in 720p/60 on both a Princeton AF3.2T and Sony VPH-D50HTU front projector. Both support 720p and 1080i. The source STBs were the Panasonic TU-DST51A and Samsung SIR-t150, both of which also support 720p and 1080i.
To me, "The Practice" doesn't look as sharp as "Alias". I attribute this to the use of low-light techniques, high-grain 35mm color negative film stocks, and shallow depth of field - all cinematographic elements of "The Practice".
It could also be a problem with 35mm film to telecine or datacine transfers.
I have seen varying quality in 1080i material, both live and transferred from film.
To my knowledge, there are no HD cameras equipped with CCDs of higher resolution than 1440 x 1080. There are, however, 1280x720 cameras.
For the reasons why ABC decided to go with 720p transmission, here is a frame from a presentation I have made on DTV at the past three INFOCOMM shows:
1080I VS. 720P TRANSMISSION
1920 pixels x 1080 lines x 30 Hz x 16 bits = 995.3 Mb/s
1280 pixels x 720 lines x 60 Hz x 16 bits = 884.7 Mb/s
1080i & 720p broadcasts are 4:2:0 MPEG
1080i compressed 51:1; 720p compressed 46:1
Fox carries this one step further by showing that 480p High Level, Main Profile MPEG-II is compressed only 16:1 before broadcast, so it is a perfectly viable format for DTV and represents a substantial improvement over 480i NTSC.
One last thought. The majority of direct-view TVs and rear-projection TVs do not have enough resolving power to show all the detail in a 1080i picture. Certainly not with .6 to .8mm dot pitch in a direct-view CRT, and 7" tubes in the RPTV sets. So the argument is largely moot from a technical standpoint.
Pete