Yes most older movies not shot in HD may not transfer to BD as well, or with the quality you would expect from BD. They still look their best ever and sound best also. Just saw Braveheart on BD and it was pretty good. Dolby True HD sound track was really nice.
Movie sets, props etc. have to be extremely well made - take for example Predator 2... from ok to really cool looking on VHS... than I bought it on DVD, not even BR, and the movie fell apart like a hottie without make-up the morning after... a movie like Braveheart seems to be A+ from the production value so it doesn`t deteriorate noticeably... but my beloved B movies get killed by the high resolution. Another victim was Aliens - the tech-props and soldier stuff seems laughable in HD...
on the other hand movies like the original Alien and Predator age pretty well... a testament to their creators...