Yeah I understand all that. But the game should upscale the 720p image to 1080i like Uncharted does. I was surprised to see 1080i as the main resolution on the back of the box. Bottom line is, with my older TV, I have no choice but to play the game in 480p which blows.
That's exactly what the PS3 (and xbox 360) does, it upscales 720p images to higher resolutions. Which means it still renders the image on a 720 resolution.
Now I don't have the game for either of the consoles, but I imagine that if it says 1080i on the back then it means that the game supports a 1080i resolution mode, it doesn't necessarily mean that the game is always on 1080i, it probably depends on your TV or monitor.
But like I said, I don't own the console version of the game so I don't know.
You should also know that not all monitors support interlaced display modes, which would certainly explain why you can play the game on 720p but not 1080i.