A two stroke is a bit different than a four stroke. Fours do require periodic maintenance and will require rebuilding long before a two stroke, but primarily the valve train.

I think if the engine is treated properly, and the valves are kept adjusted, then the time between rebuilds will be lengthened substantially. Depending on the engine, it seems to me that resetting the valves should be done every 100 hours max. But rebuilding is so infrequent that not too many hold onto the engine long enough for it to be necessary.
Dennis-