Seb Downey has confirmed that Killzone 2 natively supports 1080i. Here is the quote:
"I got a message from one of our code gurus today about me talking about the 720p stuff I was spewing incorrectly and told me that we now support 1080i natively too. Glad they got that in too. Now rejoice!
Seb Downie - QA Manager - Guerrilla Games"
Seb's response to a poster that was concerned about the vagueness of his "native" statement:
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."