This is a great comment. I'm pretty sure every non-trivial website would be better specified (as opposed to HTML) in almost any measurable way (LOC, clarity, etc) in say raw opengl.

Yes, creating a UI in an immediate mode tech would be pretty hard - still easier than HTML/CSS.

I'd love to see someone prove me right: Take any non-trivial site like twitter, facebook.com, whatever and reproduce it with opengl/d3d or whatever. I bet it will be less LOC (incl all the libs the source website includes), more clear, easier to extend, faster to draw, et cetera.