Dolby Digital and DTS are both lossy compression formats - there's no way to entirely get around that. There was a post many, many moons ago in this forum from someone who had a chance to stop by soundhound's studio and listen to both the Dolby Digital track from Superman and the original raw audio files that were used to create the DD track ('hound did the audio work for the DVD that was produced back around 2002 or so) - the poster was positively depressed at the differences that existed between the original multichannel PCM sitting on 'hound's hard drive and the DD track on the DVD. Lossy compression loses stuff. When you put a DD or DTS track up against lossless music formats like CD, DVD-A, or SACD, you're creating a situation where the only way for the lossy format to win is for someone to screw up the mastering of the lossless track somehow (which, with many new CD's these days and the elevated levels they are mixed at, certainly can't be ruled out).

All that having been said, I agree with BloggingITGuy that the mastering plays a big role, and I've gotten some pretty enjoyable audio from movies. It probably helps that audio in movies can work in concert with video - doing a good job (the best possible with the "lossy" tools available) in conjunction with good photography and video mastering can lessen the overall effect of compression on the viewer's experience.