Actually, I've had an aviation A&P mechanic tell me the exact same thing about small aircraft engines. He remarked that the TBO (time before overhaul) times actually achieved by owners who flew regularly (like at least once/week) were better than the owners who let their aircraft sit for months at a time, came out to take the plane for a "$100 hamburger" and then let it sit months more.

His theory was that the lube drained off the cylinder walls completely when it was allowed to sit for months, making the initial startup much harder on an engine that was used infrequently over an engine that was used regularly.