this whole issue is very nebulous. different manufacturers likely have different ways of interpreting power. the question "how much power can a driver take?" is actually quite a complicated one.
one consideration is the thermal limit. that is, how much power can go into a driver before it blows the voice coil. this is, obviously, key, because this is sort of an event horizon-once you exceed this, there's no turning back.
the other consideration is the displacement limit. now this gets fuzzy. this is where alot of manufacturers fudge. all speakers are at least weakly non-linear, and, when driven to excess, become even more non-linear. what that means is that distortion tends to increase with increasing power. you can exceed a displacement limit and not exceed the thermal limit and what do you get--alot of distortion.
but it's not like the graph of a drivers distortion is a step function. distortion is relatively low through the lower portion of the driver's power range, then at some rate, the driver becomes more non-linear and more and more distortion occurs.
different manufacturers quote different displacement limits because they pick different acceptable distortion levels-5%, 10%-often they don't even say. so, the same driver could be rated at different power levels by different manufacturers.
the moral of the story is that published specs are a good starting point, but not really all that helpful. usually, most drivers distort prior to melting so you can get an idea of the driver's ability this way. (I'm NOT saying you should drive your units to audible distortion-unless you want to kiss your tweeter goodbye.)