Full length animated movies are not really the norm for Japan. They like their TV series far more, though for what reasons it’s hard to say for sure. Be it funding, or marketing or even reasons of plot, the point is that Japan makes far less movies than series. And what movies are made don’t all get the chance to see the dawn of international sales. Most stay right where they are in Japan.
However, from what few movies do make it to the US, there’s little doubt that when it comes to ratings, movies have far more free reign than their series counterparts. As seen in the Air movie version, more nudity is included, and there’s even a huge shift in tone from the original series. Other movies, many of which begin as OVAs, such as some of the Sailor Moon features, the Kaleido Star specials and even the Fullmetal Alchemist movie contain more fanservice and/or violence. Without the pressure of meeting the demands of a particular TV station, movies can often veer where they will, sometimes increasing inappropriate content in spades (such as is the case with the Revolutionary Girl Utena series and movie).
Thankfully this is not a sure cause and effect. While some movies do their own thing, not all do. A few movie features keep pretty close to their original series versions in respect to content, such as is the case with the Gundam Wing movie. However, it is something to be aware of when planning on watching a new movie version of a show you love and considering to bring in family members to the viewing experience. Often we think that “re-telling” and “continuation” mean just a shorter version of what we already saw in the series, but with Japan that’s not always what you get. What may have been PG in series form might end up as M in movie form. And, no, the “M” does not stand for movie.