The A340's advantage was it was here first. But some airlines that fly the A340 (like Singapore and Air France) are trading them in for the new generation 777s that equal or exceed the A340s payload and range because the 777 offers better overall economics. The A340 is more of a "stretch" A330 then a brand new "clean sheet" plane - a criticism that EADS often lobs at Boeing. The 777 is a "clean sheet" plane, and has the advantages of being so. Just as the A380 is a "clean sheet" plane compared to the 747-400, and has the advantages of being so.

Airbus has said it plans to offer the 7E7's engines on the A330, but Boeing has the advantage over the A330 that the A330 had over the 767 - years of seeing how the competition fared in service and tailoring their plane to correct as many of the difficienies of the competitor as possible to make it more appealing to airlines.

So a 7E7 will most likely do things an A330 can't, and/or do them better, which will add up to enough of an incentive that airlines will choose new 7E7s over new A330s and may replace older A330s with new 7E7s instead of new A330s.