"losing usable height is more of a pain than losing width on widescreen displays"
For you, maybe - not for me. Application menus also commonly sit in/alongside a taskbar - and the fact that text runs horizontally in my locale thus becomes relevant.
For what it's worth, I run a minimal window manager (Fluxbox), configured so that application (and other) menus pop up on a keystroke, along with a minimal taskbar and desktop pager, and a set of monitors (Gkrellm) occupying a narrow vertical bar. (And no desktop icons - useless for me, as they'd almost always be obscured by windows.)
Personally I never got on with anything in Unity, but of course your mileage may vary - and that's the point: the great thing about Linux is that you get the choice of a desktop configuration that works for you.