I guess what he means is the possibility to change the thrust rating with a push of a button while on the right FMC page as is the case for all 737 models from the -300 on (no execute needed, it is active immediately). Most other boeing models seem to have the ability of fixed derates as well, so that is not a 737 only thing.
The 737 works exactly as Old Smoky describes for its big brother, however on the classics you do not have any protection and can overboost the engine when firewalling the thrust levers. On the NG the EEC protects you against that. However when derating and using performance figures for a derate you have to be aware that firewalling might put you into an uncontrollable state as the VMCg and VMCa are different for each derate setting.