I guess it boils down to how much extra server load it's going to add to make all markup user definable, rather than just sigs. I'd guess that if the signiture controls are OK, then it's probably not going to be a big deal to introduce something similar for posts (though people may want different things enabled for posts than for signitures).
/me summons the mighty powers that be. (read: waits patiently).
Everyone got along fine on BW/GAME without the colour, font and size tags. They have no great use, if you want to highlight something you can use the bold, italic or underline tags. The colours look really bad (especially on the green background) and serve very little purpose.