It is not only a first class issue (but it is happening alot of the time), although we upgrade whenever we can, when we sit in coach on 3 across we book the window and aisle, as neither of us wants to sit in the middle. I have had gate agents move the aisle to the middle so we could sit together...and I make them move it back...and often have some couples split middle/middle and one of them wants my aisle seat...kind of like people wanting me to put my carry on under he seat in front of me so they can fit theirs in the bin.