Speaker wattage question

Why do speaker manufacturers put it in the specs when you can possibly drive anything with 1000wt of clean power?

If the speakers are rated to be able to handle 200 watt/ch continuously and I am using 1000 watt/ch amp, how do I know where those 200 watts are, speaking of volume? 

My speakers are rated 15 watt - 200 watt. Before I was using 60 watt amp, now using 120 watt, and it is definitely better, though the quality of the current amp is higher as well. I sometimes listen to jazz/rock fusion at relatively high volume for couple of hours straight - nothing happens. The amp feels very relaxed and so do the speakers. In the case of the speakers that I have I wouldn't want to stay closer to the 15 watts than to 200 watts.
That math is too complicated for me. But the question was not about the precise figures but about real life situation and the position of the volume control. Anyway, I guess that this is the kind of situation when you cannot just rely on your hearing not to damage the speakers.
It appears that as it is often the case there is no general answer, it all depends on the particular application. One thing is certain though - when choosing speakers first choose quality drivers not nice cabinets and fancy crossover work.

Of course, all three elements must come together to make good speaker, but drivers come first, that's the start.