No doubt the parents should excercize greater judgement and do share the responsibility. But the Hotels share some of the responsibility as the distributor of porn to make sure they are not selling it to minors. Hotels can easily take this step and a couple posters indicate that some already do. If I am going to sell alcohol, I have to do everything I can to ensure I am not supplying it to minors. The same should apply to Hotels distributing porn.
First, I have yet to see "porn" in any hotel. While some of the stuff might come close, it is not porn, at least not based upon the community standards in most of the places I travel. Second, the hotels are not selling those movies to minors. They are selling them to consenting adults who have to go the extra mile to order the movies so as to minimize inadvertant exposure. If a minor is able to watch porn, then its because mommy and/or daddy aren't doing their jobs.