Because you need a fast raid system to access 3.5tb in 18min. It has to be able to read about (3'500'000/18/60) 3'241mb/s. A normal consumer hard drive is still below 150mb/s. This means at least a 20 disk system...
Edit: Also remember, they built the system in 2005 when disks were smaller and slower than today.
Even if it did require 20 disks those things feel like they weigh a pound each, let's say 2, that makes it a total of 40lbs. Big difference between 40 and 600. By the time the PS4 lumbers its way into existence there will be fast enough hard drives with high enough capacity. The problem will be the medium which they sell games on. All games would have to be installed since of course the medium which the games will be stored on will not read fast enough.
As for your edit, how is that relevant, wasn't that absurd "600lb" statement recent?
You're most likely correct taking into account that its a bidding system to get integrated in the console. Hopefully MS and Nintendo release their systems first, only to find Sony held out for Quantum processors. (A lot can happen in 5 years )
2 things. 1)ITS UNCOMPRESSED VIDEO of course its going to huge. 2)3.5TB fits on 2x3.5" hdd, weighing 2 to 3 pounds each... Why in the world would it take 600LBS?!?
I also 90% sure the PS3 can handle SNES at UHD resolution, 60fps. PS4 WILL support UHD, but don't expect intense video games to use it. (Take for example MGS4 for PS3 (720P title released fairly recently) )
I highly doubt Sony would waste money by adding UHD support when no one buying their consoles would make use of it. I mean.... can you honestly imagine the graphical requirements to display a higher end PS3 game at that resolution?
I never seen a UHD in real life, but hope to see one in the next years on some conferences. I don't think this TV's will be for private customers available in the next few years. I mean, who of us have so much space to stand there a 70" - 90" ? Let's wait and see what the time will bring.
People with absurd amounts of money maybe, that's about it. The video is uncompressed because it reads faster.