Well I was going up for a couple of business meetings and it was really not pleasant being surrounded by so many people just off long haul flights!!! A few showers in the public toilets wouldn't cost BAA much to install, especially if subsidised by the airlines...
It makes sense for there being a lot of O&D traffic because it only takes 3 or 4 hours to drive there and it's also quick and easy to take the train. I live right next to Heathrow however so it's easier for me to fly, plus the train was £180 while it was only £115 to fly.
Yes, it's just BA
that fly to Manchester from LHR
and in fact I don't think there are any other airlines that fly to Manchester from any London airports. Sleasyjet fly to Liverpool which isn't far from Manchester, but i think that is about it...please correct me if I am wrong!