[quote name='darthbudge']Because most likely the BR version has uncompressed HD video and audio, whereas the DVD version had compressed SD video and audio.[/QUOTE]
Just saw this post. HD video on Blu-ray is not uncompressed, it just has more data than SD, due to the higher resolution of the image, hence the need for a larger disc capacity to store it. It uses newer compression types, VC1 (or WMV HD) and AVC (or MPEG-4 Part 10 or H.264), in addition to higher bitrate MPEG-2 (which DVD also uses, and which was mainly used in early Blu-rays), for compressing the video image. The new codecs allow better compression ratios than MPEG-2.
Also, many of the newer Blu-ray discs also have compressed audio, albeit lossless compression, such as Dolby TrueHD or DTS-HD Master, rather than lossy compression, such as Dolby Digital (and DD+), or DTS (and DTS-HD HR). Some Blu-rays do have uncompressed Linear PCM (L-PCM) multichannel audio tracks on them, although they seem to be much less common than when Blu-ray movies first started being released. This is in all likelihood because more of the current generation of Blu-ray players and HT receivers can handle the lossless audio, with HDMI 1.3 allowing bitstreaming of the high-bitrate audio over HDMI to a receiver that can decode the tracks. Some Blu-ray players can also decode the lossless compressed audio formats now, and pass them via HDMI or multichannel analog outputs to a receiver in multichannel L-PCM.
BTW, I paid $55 for Band of Brothers Blu-ray in a pre-order from Warner Video, and sold my DVD version when the BD came in. Well worth the money I spent, and definitely worth what it's going for on Amazon and at BB.