The thing about Morrowind, Oblivion and Fallout 3 is they all run on the version of gamebryo that Morrowind originally ran on. Each new game they just made some improvments but it was the same basic tech. This time around new Gamebryo, with improvements. I'm good with that
Umm, Morrowind was mainly developed with Netimmerse 3 but got Netimmerse 4 slapped on just before it shipped. Oblivion and Fallout 3 use Gamebryo 2.x (Netimmerse 6).
There's quite a difference between Netimmerse 3 and Gamebryo 2.
Gamebryo isn't really the issue here either, it's a good engine, it's more about being able to use it well and take advantage of it at the fullest. As StoneFrog said with the Havok comment, it's just a matter of fine tuning their skills with it more.
Anyway, don't really expect any drastic changes in the next gamesas game, it will no doubt still be a PC/360/PS3 game and still use the same tech as Oblivion and Fallout 3, even if it been improved upon like how Fallout 3 was improved upon Oblivion. We will probably not see a big engine jump until the next console generation. Reusing stuff is cheap.
But it would be cool if they started to use the ID Tech for their RPGs after their current game, even if they probably will have to change it a lot to make it suit their needs.