My tivo outputs 480i and 480p for for SD tv shows, just depends, and I also have the tivo set on Native.
Like I said, tivo community guys have commented that its a 1080p file, which if so, 1080p/24 can be a smaller file size with the same to better quality. The broadcom chips can accept a 1080p input, they will just output 1080i. We saw this as Dish Network made 1080p tv shows avaiable for download, but the software of the hddvr was not quite right, so it only output in 1080i. Im wondering if we wont see a 1080p update to the Tivo's.