The macbooks do not have a mute switch because when they are closed and in sleep mode they do not emit audible notifications like the iPhone and iPad do.
So when people are in meetings everyone has their notebooks closed and in sleep mode, right? Some boring meetings these must be... I thought everyone had their notebooks ready and on the go to take notes, present something, record something, etc. etc.
Iphones and ipad don't emit audible notifications when they are closed and muted either. So if you want to silence a macbook for a meeting you close it, if you want to do so for an ipad you put it to sleep and mute it, simple really. If you have any of them running they are equally prone to emit audible notifications, but somehow one of them doesn't have mute switch you just have to mute them via the toolbar or keyboard.