you're right. that statement may be misleading. If your quality score increases, an adwords rep will tell you that will bring your cpc down, and I have seen that, but it's pretty slow to happen. Changing the max CPC will change things much quicker.
Let me clarify a little:
Quality Score & Max CPC
We don't know our quality score. But we do know that if it is increasing (by looking at min. CPC) that we don't have to have the same max CPC to maintain the same ad rank. We don't know the actual weighting of that side of the equation, but we know there is some relationship that we can test.
Max CPC & Actual CPC
We also know that max CPC has an effect on actual CPC, in that when max CPC increaes your actual CPC will most likely increase.
thus. if quality score is in fact increasing(which you get by looking at min. CPC) you should be able to decrease your max cpc, maintain your ranking, and pay less.
This is definitely important if there are few bidders or you are bidding top placement.
**also worth noting again is there are WAY TOO MANY variables to try to get any exacting information. We don't know what we don't know. So all we can do is test and see where our lowest max CPC keeps our ad rank the same.