Paul, I think unfortunately, some rights owners have the attitude of, "We'd rather make nothing than take a risk, or we'd rather not put out a release than put out one that only barely breaks even."
In other cases, there may be rights issues that prevents the films from being released region-free. If Company A owns the release in one territory, and company B owns the release rights in another territory, Company A may be restrained in its ability to put out a region-free edition, even if Company B has no desire to do a release for the area that it has the rights in.
I think some studios are really making good faith efforts to get releases out as best they can, and operate under the idea that it's better to have 50% of something rather than 100% of nothing. But not everyone feels that way.
It does seem like more and more titles are being made available in HD via digital distribution that otherwise aren't getting released. Whether it's Netflix or Amazon Prime, Vudu or any other service, I've rented titles online that streamed in pretty decent looking (and in some cases, great looking) HD that may never get disc releases. It stinks when it's one of your favorites and you can't get a hard copy, but that does seem to be the way things are going. I'm startng to feel like I just have to accept that and go with it, otherwise I'll never get to see certain titles in HD.