Haven't read the whole thread so sorry if I repeat what others may have said already.
I do make my children say sorry and also I'd expect the teenagers that I teach to say sorry if they have offended either myself or another member of staff. Saying sorry is a social convention that makes the world a slightly better place I believe.
I don't want it said just as a meaningless grunt though and would expect them to elaborate on exactly what they are sorry FOR and how their behaviour may be different next time in order to ensure that things don't escalate.
It worries me that some people seem to thnk that apologising is a sign of weakness - it isn't; I believe it's a strength to be able to say "okay I accept that I've done such and such, and through that have hurt your feelings/made you angry, whatever - and this is my way of beginning to re-build the bridges between us".