I have an original Schitt Aegir (20 w/ch 8 ohms) and a pair of Ohm 1000 speakers in a 15' X 24' room with a vaulted ceiling -- absolutely no problem reaching my desired listening level (85 dB average) with no hint of clipping or compressed dynamics. Two caveats, however. First I use a powered subwoofer and roll off the deep bass to the Ohms. Deep bass can be a power hog Second, as many know, the relationship between watts and volume level is logarithmic, not linear. Doubling the power gets you 3 dB more volume. Doubling the perceived volume takes 10 times more power. So, if you are a headbanger, and have medium or low sensitive speakers, or have a large room, you're going to need a lot more power than I do.
But, as others have noted, lotsa watts are an attractive advertising carrot. And Class D amps have made it easier to offer that carrot these days.