Close your eyes and count to 80.
Most human beings have 10 fingers and 10 toes. Therefore the number 10 is a big deal to us. We use a base-10 number system, bestow honors in top-10 lists, and think in multiples of 10. So it's inevitable that makers of surround receivers have fixated on the number 100, or 10 times 10. For some of them it's the minimum power-output number allowed on any spec sheet, whether the amplifiers measure anywhere near that level of performance or not. Anything beyond that is likely to be in multiples of five (the fingers of one hand): 105 watts, 110 watts, 125 watts, etc. The more you become aware of this compulsion to express everything as a function of our physical form, the more comic it gets—humans are so self-absorbed. Or am I just projecting?