Movie ratings on cable guides

[anotherguy]

I have a question about the ratings for novies on cable guides for basic channels. I've noticed that movies will be listed with whatever the rating was for when it was in the theater or on video, rather than whatever the actual TV rating is. On a movie that was originally rated R but was edited for TV to where it was either TV PG or 14, it is still listed as R on the cable guide. Then there are also movies with the rating NR for not rated, which could be anything from kid's movies to porn.

I have Charter Cable and they use TV Guide's cable guide, but I've also noticed this on Dish Network when I had it as well. Why don't they use the TV ratings rather than the theatrical ratings?