Bear in mind not everyone has a full band. If it was you and an acoustic guitar, no srums… would you really want a large loud amp… or something small. Different music, different venues, different sound men!
Also bear in mind that Wattage doesn't always relate side by side with different amps. If you play through a 150W EBS Drome combo, you will find that it is actually LOUDER (and cleaner at loud volumes) than many 300W amps… Its down to the technology used. The different being that the Drome is £800 odd for 150W combo!
Shep