I beg to differ, I have catered QF aircraft (737's) with both front & rear doors active for disembarkation! Normally we would use one truck to do both front and rear galleys, but if a flight was running late we would use two, in most cases the aircraft would be fully catered before the last passenger had disembarked.
Fair enough Howard, but I know that QF looked at the B737-900ERs and decided against ordering them because of the excessive transit times.
The "ditching" scenario on the -900 would be interesting in that the rear doors are unusable (because the tail sits too low in the water (like the -800)) and therefore there is a very large number of people from the rear section scrambling forward to the overwing exits. Could become very chaotic.