The bitrate could easily be lowered to allow a lot more video on a disc (just like you can make a 4-hour DVD video, it will just look like crap), and with 50GB discs a full season, say 13 22-minute episodes shouldn't be a problem. That wouldn't leave much, if any, room for stuff like additional audio, commentary, bonus scenes, etc. It's also probably cheaper to make two 25GB discs though, so that's how it's typically done.
I also think the companies making said TV show series on Blu Ray think that people will justify the price more if they see that it's 3 or 4 discs.
We had this discussion endlessly on the blu ray forums before I got tired of the BS and left. Basically it boils down to two things. Studios are snobs about quailty more than average consumer when it comes to the discs so when they release something like a TV season they always use the highest bitrate they can never the opposite. They only lower the bitrate as a last measure to cram in additional audio commentary.
With SD content you can fit an entire season on a single Blu Ray disc pretty easily IF you stick with just SD resolution and DVD bitrates but because even in SD Blu Ray does allow higher bitrates, and much better quality, less compression, studios normally just opt for the higher bitrate to provide a quality product, and in the case of SD content because DVD is cheaper they just release most of that on DVD anyways.
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he main issue is consumers hear Blu Ray they think HD so studios go with that, if it ain't HD they are reluctant to release it on Blu Ray even if there are benefits to the consumer, Blu Ray supports vastly superior audio as an exmaple to DVD but again even with high bitrate low compressions SD content with uncompressed master HD Audio
average consumer will not care they will stick with cheaper, "sd-DVD" and reserve Blu Ray for the quality stuff.The other MAIN reason studios choose to go with more discs over fewer every time is value perception, the consumer thinks they are getting a better product because more discs = more value. This was one of the reasons why LaserDisc fans chose to go with the 30 Minute discs instead of the 60 Minute discs that require less swapping, more discs = more value plus they wanted the bonus features.
As for Blu Ray recordables, I was curious if anyone else bought into it. I wish I hadn't I have a ton of unopened packages. Even when I bought it I knew it wasn't worth the space to cost ratio but I felt like it would even out eventually and I was all into DVD because despite how cheap Hard Drives are now I still like having a physical back up that is less likely to become corrupted or suffer from hdd failure or whatever else could happen. I store everything on hard drives but I still back it all up to disc. I also have spare hard drives just in case because data loss is a bitch and I don't trust cloud storage because there are times when I don't have access to the internet even still.