Because BD = Sony in many people's minds.
There are still people in the US south that are bitter at the north because of the war in 1860's.
MS would be foolish not to use BD, a cheap established 50GB optical format that comes with HD movie playback. Why invent or use something more expensive or with less features, to spite the BD group?
Perhaps its because BD is slow as heck and many of us think we will see 4-8 gigs of system ram in next gen systems.
RIght now at 2x bluray trasnfers at 9MB/s. The ps3 has 512MBs of room. That means it takes 57 seconds to fill up that ram. Thats almost a minute.
however lets assume in 2011 we have 12x blurays at at transfer rate of 54MB/s with 2 gigs of ram is 37 seconds , 4 gigs of ram doubles that 74 seconds and if we are lucky enough to get 8 gigs of ram you double that again 148 seconds.
Those are not good trasnfer rates , thats also if they can even make a 12x bluray drive and of course thats with the disc spinning very fast and making lots of noise , a complaint thrown at the 360 and its 12x dvd drive often.
Now lets look at expanding the disc to store more content. Dual layer discs are 50 gigs. To get to the 400 gigs some peopel have said in this thread your looking at 16 layer discs. What exactly will the read speed be as you go deeper into the disc ? What would the switching cost be for moving deeper down the layers ?
I don't know how good of a format bluray is for a continued gaming format.
Now perhaps toshiba sitting on a format that isn't being used they could possibly tweak hd dvd to meet the requirements of a next gen system. HD- DVD was a format created for launch in 2005. In 2011 i'm sure they could do more with the discs. 45 gig tri layer discs should be more than enough with todays compression. What i wonder about is transfer rates. If toshiba could increase the transfer rates to double or tripple what they are with bluray/hd dvd it may be a no brainer for MS esp if disc costs are low.
I'd wager that 20MB/s would be good for a 1x read speed. Ship the drive at 6x and your looking at 120MB/s that would fill up 2 gigs in 16 seconds , 4 gigs in 32 seconds , 8 gigs in 64 seconds.
Of course I'd say they just go with SDXC if they are going to use a format other than bluray. It is flash based and will go to 1TB but it has transfer speeds starting at 104MB/s and there are plans for 300MB/s cards.
Uses a custom verison of these not only can you crease your own format but you can get rid of a huge 5 1/2 drive from the casing. You also remove moving parts and you can add resell protection to the flash card by imprinting it with a console serial code that then either the game owner or a store like gamestop would have to pay to erase for resell.