Actually designing a full, separate UI for two different platforms means a great deal more effort needs to be put into laying out, programming, creating art and assets for, and testing each UI, so that's a pretty good reason not to. It'd be far more sensible for them to just make a UI that scales and sorts well on both platforms rather than create a unique one on each.
I wonder if that's what they thought they were doing with Oblivion. Really, Oblivion's UI is fine when it's adjusted for higher resolutions (not great, just fine...). Fallout 3's UI works much the same as Oblivion's but it seems to work better somehow...it still needs mods to fix the resolution issue though it's definitely not as noticeable with the in-your-face humungo font.
I don't know that I've ever seen a UI that worked as well for consoles as it does for PCs and vice-versa, but hopefully they'll give it some attention since I agree with you: I doubt, based on Beth's track record, that they'll take the time to make 2 separate UIs.
Good point. That's fairly tricky, though. The most significant change I can think of off the top of my head would be reducing font-size and making the UI in general bigger (this was a big problem Fallout 3 and Fallout New Vegas had - the UI was too small to fit the map at a reasonable scale)
Good point indeed. The map is a big one when it comes to resolutions and scaling, and that's been a problem in both Oblivion and FO3.