Like most things, electric will work fine for small jobs, and gas for the big ones. Until you get into the 240V high-amp units, anything you get than can plug into a 120V outlet is power limited by necessity to a 120V 20A circuit, which cannot put out the power of a 6HP gas engine, so they need to concentrate the available power to a smaller area to get the job done. Even more so with a battery operated unit. So yes, if you are cleaning a smaller area, the water will come out with just as much force, just not as much of it. In a limited space, like an engine area, that can actually be a good thing, since you just want to clean the surface, not penetrate into places water shouldn't be... and still remember to wrap or cover any electrical boxes and connectors before cleaning the rest.
Everything is a compromise... if you want electric convenience, then you get less overall power capability than a gas unit [fewer gallons per minute at a rated pressure].