In the UK (especially with PC based speaker systems) the problem is they quote PMOP - peak music output power over two channels (at least) and not per channel which is the peak-peak output voltage squared divided by the load.
Not really true - all decent equipment in the UK quotes RMS per channel - the ludicrous power claims are from cheap crap, usually PC speakers or in-car equipment, neither of which usually bear the slightest resemblance to a real value.