There probably was cheer a long time ago, but too many people were bitching that they were getting killed while cheering over dead bodies and tbagging. Valve's emails were flooded so the only way they would make the bitches happy is to disable to command, but left it there for teh lulz.
Cheer command's been there for freaking ever.
I read something about it, not sure if it's true. In beta or pre-beta you could 'cheer', kinda like taunt in TF2. It looked unrealistic in the middle of battle so they removed it.