I think SuperEgg has a very solid point, it's simply easier to read when the nick's are right aligned, and the text is wrapped to the right of the nick instead of below the nick.
Im not a programmer so i don't see all the huge issues this would spark. But i can definately say that for me it's not about anything but readability, i hate pointless skinning.
And i've tried xchat ages ago, it was buggy, crashed on me and i didnt like it one bit. So even if this feature is never implemented in mirc im not going to switch
