Widescreen gaming in RTS at 1920x1440

[moralpanic]

Anybody know why when it comes to RTS, there usually isn't 1920x1200, but 1920x1440? I think i first saw this with C&C Generals, but i've noticed the same thing recently with Warcraft 3 and Warhammer. I don't mind, since it looks fantastic at 1920x1440, but i've always been curious.