There are no 1080p sources everywhere, let alone 1080p24 so you are talking about most likely 1080i or 720p source first scaled then frame rate conversion with optional deinterlace... all this has to be done properly, very high-quality
on-the-fly, in a desktop player. (For comparison I use
this plugin kit in Fusion and it takes very long time on dual-core workstations...) BTW I'm not sure every 1080p TV would be equally OK with a 1080p24 source...
We're talking film here, in which case, you're completely wrong.
The HD discs are mastered from D5s which are 24p from the film.
D5s are about 300 Mbits/second if memory serves me correctly, but not truly lossless encoding. That's what is encoded to go onto the disc.
So in fact HD-DVDs and Blu-rays
are 24p sources assuming the original was film based 24p. Not only that, but they're
stored as 24p. So to output 24p, you really do just have to output the unprocessed frames. Getting anything other than 24p you have to go through the telecine process in the player. This is for 1080i/60 or 720p60.
How do I know? One of my best friends works directly on the VC-1 encoder. He spends about 1 week in month in Hollywood working directly with movie studios and production facilities to improve the encoder.
Let's talk some more about the lack of 24p sources when you're ready.