RMS means Root Mean Square, not continuous power.
Even radios that say 18-22w RMS are lying as these ratings are usually given at 14.4v and 1khz, the easiest frequency to reproduce. Take an oscilloscope, mulitmeter, and throw in a little Ohm's Law, and WaaaLa! You won't find a deck on the market that realistically does more than 10-12 watts.

I would take a 20w x 4 outboard amplifier over a 50-60w x 4 deck any day. Open up a deck and look at the amplifier section of the circuit board. Look at the size of a 20-30w x 4 amplifier. Comparing a 2 inch by 2 inch square to a 10"x10" amplifier is like saying a Briggs & Straton lawn mower has the same Horsepower as a Corvette.