Todd has stated every time a ES game is created, they start with a blank slate. So every time the create a new project the engine has to be overhauled (as to keep with the generation) and that alone takes a significant amount of time. (Don't say graphics don't matter) After that (and during that development) art style is developed as with the content that will actually be in the game. Everything that is put into Skyrim is remade from scratch. So every quest line, every piece of armor, every weapon, etc. has to be redone. To incorporate everything from the older games and also adding the new things isn't possible within a timely manner. In the business there is a finite amount of time a project can continue before the funds for development are gone. There is a point when they have to say hey we cant add anything else.
Personally there are things I will miss, But the fact is to have a NEW game, things will have to go.
The team had a vision to make a new game with certain features and story lines, Reimplementing old stuff is second to the current ambitions.
I still think Skyrim is going to be a fun game to play, but then again I view it as NEW game that is not Oblivion or Morrowind.