It has been said so macuh about this subject!!!
As World Traveller says, I do not think the ROC is a sales argument. Something which is much more important than the rate of climbing is taht the a/c is going to keep flying, for the longest time possible, with the least expenses possible.
In reference to Michael Schumacher, a journalist said once: “The best champion is the one who wins as slowly as possible”. Actually, he was the first with 20 laps to go, 35 seconds ahead, and at the end, his advantage was only 5 seconds. Does it mean that in 10 more laps he would have lost his race? Or that he managed to keep the first place taking good care of his engine, which could have been burnt if kept continuously used 100%?
As for my cent of info, here, and comparing Airbus' on board computers to the above experience in F-1, I have read, not too long ago, (SabenaPilot, where are you?) that modern airbusses (actually all of them except the older 300s/310s), are designed for being economic, and equipped with some kind of calculator reviewing continuously the optimum thrust/economy ratio. The result of such a continuous check from the computer results in some kind of “standard COR” (meaning that an empty A340 won't climb faster that an MTOW one), because the thrust is something like “the-less-possible”. As a result of it, too, 100% throttle does not necessarily mean 100% thrust.
From my own experience, it makes sense since I have jumpseat taken off in a B737-400 and in a last generation A300-600R. This could be a logical explanation: although the throttles of both airplanes were “full-forward”, while the revs. of the 734 where ABOVE 100% (something close to 105%), in the AB6 they never reached to 85%. Then, at cruise level, both were flying 80-82%. I must confess that it happened before I had read anything of it all, and I didn't give any importance to it since they were so different A/Cs. But now I believe it.