Just six months ago I would have argued with this statement. 1080i has half the lines of resolution as 1080p, right?
Wrong! This article does a nice job of explaining how 1080i content can be converted to 1080p perfectly.
Even though film/TV content received at 1080i can be converted back to the original 1080p content, it is contingent on your TV doing reverse 3:2 pulldown correctly. If you drop 1080i and use 1080p throughout the journey from source material to your TV set, then you don't have to worry if your TV is converting 1080i correctly. 1080p removes one level of complexity from an already convoluted process.
According to a recent test of sixty-one 2006 model year sets, more than half did *not* recover 1080p from 1080i correctly. My TV (Sony 46" XBR3) was one of the sets that failed. However, changing Sony's terrible default settings (why would they do that?) fixes the problem.
Another reason you want 1080p...when we start receiving 1080 content at frame rates higher than 30fps. Both the Xbox 360 and the PlayStation 3 are capable of 1080p content at higher frame rates than film or TV use. For these HD sources running games at 1080p 60fps, converting 1080i to 1080p will result in loss of image data. Most 360 games are designed for 720p because of the performance hit of moving to 1080p. I suspect the same will be true for the PS3. I have no doubt games will move to 1080p eventually, but currently we are not there.
I have my Xbox 360 hooked up as 1080i. Microsoft added a patch recently that gives the Xbox 360 1080p support. Unfortunately, it does not work with my TV due to a bug in their update, which Microsoft is going fix.
I am going to pickup the $200 HD DVD player for the Xbox 360. There is a lot of chatter on the internets about how Microsoft has to get the 1080p output working for the HD DVD player to compare to Sony's PS3/Blu-ray player. However, it really doesn't matter. Film is at 24 fps, and my set does 3:2 pulldown correctly now. So I will get the same 1080p output that the PS3 does, even if I am doing it via 1080i.