Of course, this could have changed in newer DVDs or DVD players; though I haven't encountered any disk which has absolutely no way of getting out of the previews, but I tend not to watch many movies.
Also, I think that I have to point out that you are entirely free to mute the DVD and go off somewhere else until the previews are done, if you're unable to find any other way out of them; "FORCES" is a bit of a strong word, given that you were not (I assume) physically prevented from leaving. This is, of course, not an acceptable solution, but it does eliminate the discomfort of sitting through previews.