I dont exactly see mirc needing a complex mathmatical operation. Yes, as you pointed out, mirc has included variious things to "enhance" the chatting experience, but if you've noticed none of them go dramatically away from chatting. Most are things you can do while you chat, not instead of chat. Listining to music, transferring (legal) files to each other, etc.. A mathmatical addition to do precise calculations doesnt really have a place in the IRC experience IMO. Though it may be convenient, its not entirely practical.
If you do need the extended math, try a dll or perhaps /run calc
