Game resolutions on PS3?

[ellldiablo]

let me first explain my setup, sharp lc46d64u, ps3, hdmi. this is the first hd set that will display incoming resolution, so this is a newly found oddity to me. old setup was a 51" sony hd crt. I'm playing assasin's creed which according to the display info on the cover has a max res of 1080i. when i play it, it plays at 720p. cod4 has a max res of 1080p and when i play it, it plays at 720p. the only way i play these games in thier max res is by changing the availible res on the ps3. am i missing something or is this the norm for all ps3 games? iv'e only noticed this recently since i did not have resolution info on my display before.