[Adam]

I just read over all of this more carefully, and there were several solutions already posted. They basically fell into two categories: some DVD players allow this to be turned off, and some devices already exist that actually do manage to remove this from the video signal (but not all of these work well).
Unfortunately, none of these are particularly cheap options, unless you already have one of the players on that list.
About half of the DVDs I have don't give me the retrace lines, so I guess this means that they just don't have the copy protection, but there doesn't seem to be a way to tell this in advance, without actually playing it.