Just to add one more possibility to John's excellent list:

It is reported by some that the 150 has a wider dispersion than the 100.

I haven't heard a 100 and therefore certainly haven't done a comparison of the two. But my way of thinking is that out of necessity, sometimes people in a smaller room have to sit more off-axis than in a large room due to furniture placement issues.

FWIW, I have a 150 in my 13' square room (albeit mated to 60s) and have no regrets choosing the 150.

::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::