I don't know if anyone actually got it to work in 1080i (Tsori seems to have), but I think it may as well be just a printing error. I've got a european version and it says nothing about 1080i on the back. Maybe the printers in the US of A confused it with the 360 version which, as far as I know, does support 1080i. If Tsori confirms that he played the PS3 version in 1080i though, it'd mean they either shipped two versions of the same game or, far more likely, a bug is at hand which could be fixed ... at least in theory. ^^
Tbh it only worked for me as i tried it on a cheap 19" from tesco which wont support anything BUT 1080i, even 480/580 that the ps3 defaults too. In this case, when setting the display settings on the ps3 automatically it unticks everything but 1080i, including the default 480.
Sorry to say however, most HD tv's will support standard definition, and therefore the ps3 wont let you uncheck it.
Overall though, as i mentioned above, and as some have found out, the screen size when in 1080i is stretched and deformed to the point where its unplayable. The screen cuts off parts of the screen so much that you cant see any of the menus, just the right hand edge of it.