Windows is not Microsoft's main source of revenue, they have something like 16 different billion dollar businesses.
No longer able to edit environment variables - admittingly i've never used this before, but I'm sure someone out there might have the need to.
Edit: Oh and Alt+Tabbing to switch between applications now uses a much improved interface rather than that ghastly 3D slider thing they had in Vista / 7 / 8. 3D effects for the hell of it are some of the most stupid things software developers do. They are just eye candy and don't actually improve the experience of using the software.
Early builds of Vista aside alt+tab in 7 onwards always used the style as in 10 (unless you changed the default options) - only windows key + tab used the 3D view they originally introduced in Vista. The only difference I think in 10 is that it scales a bit better with different amounts of applications running to be a bit clearer what task is what.