While taking your point Mr Torque, do you not think that the fault lies with the airlines who are trying to squeeze every last drop of revenue out of their passengers? It doesn't seem unreasonable that passengers then think up (legal) ways round the traps - if it means that the authorities then have to re-assess the standard passenger weights then so be it.
However as Wowzz suggested, the trade off for the passenger is cost saving vs comfort.