Not sure what all these unskippable advertisements/trailers everyone keeps talking about are. In all the movies I own, I don't think I've ever run across a set of trailers that I couldn't skip in one way or another. While specific buttons may give you a "this option is not available" type error, usually one of the following will work:
I rented Fast Five (BRD) from a Red Box and there was no possible way to skip. I couldn't even fast forward.