I am not convinced it is necessary, although as someone said it is cheap insurance.
I live on a beach and a lawn mower will rust out about 5-7 years no matter how often you change the oil. I never change the oil in my mowers. The wheels will fall off or deck rust out before the engine ever goes. I do check the oil level and add if needed ( rarely )
I've got a 8-10 year old power washer with a 5 HP Honda engine. Think I did change the oil once. Runs like new.
Maybe if I had a 1000.00 dollar genny I would be more concerned about oil changes.
I personally think keeping good fuel / fuel stabilizer is much more important.
JMO