One other reason might be that they want to sell the shows to PAL territories and converting from 23.976fps to 25fps gives a much better result than from 29.97fps to 25fps.
If the show is in HD, it was made at 24fps. I haven't seen a show yet that's recorded at 29.97 and that's in 16:9. If you save it at 29.97 on a computer, you'll end up with every fourth and fifth frame consisting of fields from adjacent frames. It'll look like crap and you'll also have to save...