Compression does not mean lossy, DTS-HDMA, and TrueHD are both compressed, and lossless, and there is nothing wrong with compression. LPCM is uncompressed on a Blu-ray. The streaming video providers, and iTunes also provide lower bitrate videos/audio which reduce the overall size.
It isn't a myth that OSX needs 8GB, you would be mad to purchase one with only 4Gb. I have Safari with a few tabs open, and iTunes open, my MBP is using 7GB RAM, good job pretending you can do "heavy duty design work" on 4GB without significant swapping