Its interesting that the Tristar & DC10 were very similar aircraft but the former had a slightly wider cabin and generally had 10 abreast seating in economy whereas the DC10 had 9, slightly wider seats.
I've often wondered why the 777 cabin wasn't slightly wider so that it could accommodate 10 abreast seating, but it would have been less comfortable. The 350 was redesigned as the 350XWB to meet airline requirements and that is it - manufacturers will consult airlines and try to accommodate their (often differing) requirements. After all they are the buyers in an often competitive market.
The trouble is whatever the width the airlines can put more seats in. Many operators have ten abreast in 777. Air Transat are 9 abreast in A310/330s, Britannia used to have 8 abreast seating in their 767s. Inhuman but it lowers unit costs. Passengers seem to prefer price over comfort.
If you are cynical you could point out that this will encourage travel in premium economy which is generally more profitable for the airlines.
P.S. Any bets as to when an airline will install 11 abreast seating in the A380 main deck? I bit it will happen although I hope I'm wrong.
Last edited by Peter47; 16th Oct 2015 at 11:12.