I'm not convinced. The filesystem layer on Linux and FreeBSD (and probably other OSs too, though I don't have knowledge) is totally object-oriented and written in C.

Gnome/GTK also encourage an object-oriented style in C, via GLib and GObject.

Also, Greek numerals were just as unwieldy as Roman ones (if not worse), and at any rate the Greeks did not use numbers in their mathematics. There's an enormous amount of math you can do without arithmetic and algebra.

(Edit: Saw your username after I posted this and I want to say that I respect you deeply -- I don't know of anyone else who has written a working C++ compiler almost by themselves. And I like D a lot, though have only had a very limited chance to use it professionally.)