SImple answer: no, not all Munros have Trig points on them, but pretty sure you'll find a cairn of stones at the top of each one (I'll tell you in 55 munros time!
). Trig points were used by the OS to calculate relative distances for mapmaking etc. Therefore you'll find them in places with good vantage points and you should theoretically be able to see at least two other trig points on neighbouring hills/other good vantage points. One interesting Trig is on the side of East Lomond, it's not at the summit, but about 50m South of it on the side. Presumably it's a better viewpoint than having one at the summit!