Actually, I've heard that Skyrim will be using a whole new engine instead of using the Oblivion/Fallout engine.
I heard it will be using the leveling system from Fallout 3. I hope they carry over the "Perk" system as well, with a more medieval theme of course. That was one thing I really liked from Fallout 3 that Oblivion didn't have.
It boggles the mind how Bethesda got those games through Sony and Microsoft certification.
Probably the same way they were able to recently re-release Oblivion in the form of a 5 year anniversary edition on the PS3 and 360, yet they were somehow able to circumvent Sony's rule that everything after 2009 must have trophy support. It could have been easily added in a patch, but it never was. The 360 has it. The 5th anniversary edition came out after the rule was in effect so it should have. I don't know how they got past that.
But if you have enough money I guess you can do just about anything, and its not like either Microsoft or Sony can say no to them because the Elder Scrolls and Fallout series is a big deal in the gaming world. That last thing either console manufacturer wants to do is antagonize Bethesda and risk them not supporting their hardware with those titles. So I guess they are willing to let the buggy crashprone software slide and get rammed through certification.