It is not that simple. The speaker is a dynamic system whose response to signals is not memoryless. A speaker that can easily handle a pure 4kHz tone at the maximum amplitude cannot necessarily also handle a 4kHz square wave at the maximum amplitude (a square wave distributes much of its power into harmonics). It is well known that you can destroy speakers just as easily by overdriving the output stage of the power amplifier (which leads to clipping) than by overdriving the speakers themselves.

Of course, Dell could include analogue filtering circuitry to filter out the excess power in inaudible frequencies if they wanted to.