They can claim all they want and perhaps it's possible that they are broadcasting at 1080p/30 for movies, but there's no broadcast or cable TV recorded in that format, so any regular TV will be the same on a 1080i set vs a 1080p set.

Also as far as practical matters go, 1080p/30 is the same thing as 1080i/60(60 half frames per second).

About the only time I've heard of 1080p holding an advantage is for some PS3 games that are displayed/rendered at 1080p/60, which cannot be done through 1080i.