More bollocks.
Problem with high wattage is over-driving the speakers. It's a mechanical thing...the driver can only safely move so much, and when more power than it's rated for is applied, it leaves those safe boundaries...so either mechanical damage occurs (crakced voic coil former from botoming out, ripping the spider, tearing the surounds, come damage, etc), or the coil burns out.
MP3 can only damage a speaker if you were to take a CD full of them, place them onto a dremel sanding drum spindle, spin it up to 40,000RPM, and launch the CD at it. Of cours I think anyhting that the CD is flying at would get damaged, including pets...and you yourself if the wife spots you doing this, so please don't tun your dremel tool into a weapon of mass disruption.