MTQatar,
the A300-600R is larger, heavier and is less suited for KTM operations than the A320 (at least from what I have been told) and if god forbid something happened more than 250 people could die in this crash. With the increase of flights you can use the A320 but still be able to cope with demand, and if anything should happen a max. of 152 people would be on board lowering risk of more deaths.
I suppose thats one way of looking at things, but personally i would prefer that an airline tried to deliver ALL of their passengers to their destination ALIVE!
If QR believe that KTM is too demanding, then they shouldn't operate in there!
Mutt.