Modern cars have recommended service intervals of approx 10,000 km, which even driving at an average 100 km/h is a service every 100 hours. Of course the manufacturer's "recommended service intervals" are more frequent than is strictly necessary, just as I would think that Lockheed's recommendation of a one month rebuild *every* 300 hours flying time is more than strictly necessary.
Also, yes it's a rebuild rather than changing oil / spark plugs / filters, but then again it's (a) an airplane, so safety / reliability limits are a lot tighter than for a car (b) it's a military airplane so their safety / reliability limits will probably be even tighter than for civil aircraft * (c) it's a bleeding-edge high-performance machine, not your run-of-the-mill jet, it *purposely* sacrifices longevity for performance. Formula 1 cars replace their engines completely after 4 or 5 races, even including practice sessions and qualifying that's not more than 3000km, or approximately 15 hours running time.
I think 300 hours for a high-performance warplane is pretty OK.
* Any commentard** out there who knows anything about service / replacement schedules for commercial airliners' engines?
** with affection, of course :)