I was quoting one of the technical guys that MotherH got to answer the question for him. (See below; I quoted him again for you.)
I never claimed it was 1080p. I said it can be upscaled to 1080p (ie. it can run at 1080p, even if the game itself isn't 1080p). This is in opposition to the many games that cannot run in 1080p or 1080i (ie. they cannot be upscaled) and instead will only run in either standard definiton or 720p.
Good point well made. I myself am not a tech head, so I'll get out Technology Director Michiel to explain: "we support a resolution which has lower vertical resolution, but displays 1080 lines. this is especially important for people who use 1080i on an older HDTV because the vertical upscaling of 720p can cause blurryness of the image, which is very noticeable, especially interlaced. the mode we use doesn't have that problem and it's slightly heavier than 720p (but not as heavy as full 1080p), but we have enough headroom to keep the framerate stable. It's not like we did full 1080p support, but we did do effort to make sure it looks good for those people who don't have upscalers or very ugly ones."
Hope that helps.
Seb Downie - QA Manager - Guerrilla Games
http://boardsus.playstation.com/playstation/board/message?board.id=killzone2&thread.id=56462&view=by_date_ascending&page=144