Hotkeys are fixed. Menus are fixed. No customizable toolbars, err no toolbars at all. Menus are totally cluttered and fixed.
that's not fully true. to a certain degree you can already do toolbars, custom hotkeys and your own menus with python... and if you know c you can customize everything anyway since blender is open source.
edit: the hotkeys aren't cluttered. there is a system behind them and most of them are quite logical.
Splitscreen? That's 19th century.
huh? look at modo, the unity editor or recent versions of adobe software and so on. they more and more use the non-overlapping split screen approach blender uses since over 10 years because it has proven to be much more user friendly than having to juggle floating windows around all the time.
Devs prefered to throw in new tools instead doing something at the UI. And with every new bit Blender became even more cluttered.
they didn't postpone it because they were stupid or lazy but because they had to build a big enough developer community before the 2.5 project became feasible.
