Manufacturers often "creatively" report the power ratings of their equipment, especially in multi-channel rigs. In fact they design to these "creative" ways of measuring to make products more marketable to the unknowing, not to sound good. Most use a 1,000 Hz sine wave, not music via reactive speakers when measuring. And most run only one channel at a time, not all of them. Of course the vendors here would never do such a thing (honestly).
Bottom line, many 100 wpc HT receivers only provide about 15 "real" wpc with all the channels driven.
Keep in mind that the relationship between watts (rated power) and dB (what we hear) is logarithmic. A 1 dB increase is barely perceivable, a 3 dB increase sounds half again as loud, and a 10 dB increase sounds twice as loud. So:
1 watt = 0 dB of gain (compared to the rated speaker efficiency)
2 watts = 3 dB of gain
4 watts = 6 dB of gain
5 watts = 7 dB of gain
8 watts = 9 dB of gain
10 watts = 10 dB of gain
20 watts = 13 dB of gain
40 watts = 16 dB of gain
50 watts = 17 dB of gain
80 watts = 19 dB of gain
100 watts = 20 dB of gain, etc.