Multichannel PCM on Blu-ray discs was done initially because the early players didn't include decoders for the new audio formats. It is a significant disc space hog to use, and newer releases are using multichannel PCM less and less. Where nearly all releases used PCM at first, I'd guess that now fewer than 25% use it. There are even some Blu-ray releases that are only using Dolby Digital or DTS. Over the next year, I'd expect studios to move entirely to Dolby Digital Plus (which is just an advanced form of Dolby Digital, also using lossy compression), DTS-HD, or the two lossless compression options TrueHD and DTS-HD Master Audio. The latter two can offer the benefits of PCM (no lossy compression) in much less disc space.