I don't know what program wattage means but ignore that. What speakers are you looking at?
It's not RMS for sure. Most people are only using between 5-25 watts RMS during normal listening anyhow so 150 is certainly not RMS.
A better metric would probably be sensitivity than the power handling (not that the power handling can't be useful). Also, what programmer is saying about your power source being closer to the high end of the range thingy is wrong. Look at tube amps, some of them are rated for about 7 WPC and they sound great*.
In my experience distortion is caused by having a crappy amp or power supply, crappy speakers, or trying to play speakers louder than they were meant to be played.
Power generally isn't the issue when listening to speakers at low volumes. Most AVR's these days have excellent power supplies (and specifications) so if you're using a good AVR and the speakers don't sound good then it's probably the things making noises that aren't so good.
A good power supply is a good power supply. It doesn't have to be huge to play program material well. If we look at a speaker with average sensitivity of 87db/1W/1m then you only need about 20 watts to drive those speakers to 94ish db at 9 feet away. That's without taking into account room gain as well, so this means that if you want to listen to 94db continuously on 87db sensitive speakers you only need 20 measly watts of power. However, this is much louder than most people listen to anything for very long.
The reason to have a robust power supply generally has to do with peaks (explosions, really dynamic music etc). During big peaks, power demands can reach 250 watts on up depending on listening levels. It will also depend on if you're crossing the speakers over to subwoofers or not as well.
*Theres more to tube amps than just the wattage, and people argue about tube amps for other reasons ("good" distortion). We'll just ignore that stuff for the moment since my point giving a counter example to the big wattage.
