A John Deere with No oil changes?? Duh, (and BS engineering)... I'd be putting my oil vacuum pump hose down the dip stick hole and sucking it all out as needed..
Agreed, the older engines, cast iron sleeves, roller bearings, etc, splash lubrication lasted very long. Keep it simple, less stuff to break/fail.
Newer engines, some corners are cut, but for instance, OHV's, over head cams, IS an improvement in performance, fuel use, heat dissipation, etc (like a flat head Ford vs an OHC newer car engine).
I've never had a yard machine with an oil filter/oil pump and when the oil looks darker, it gets changed. For my 10 HP Briggs generator (OHV, tilted cylinder, splash oil system), I use full synthetic 10w50 (SW Florida-so when used, it's hot and will run for days).
IMO, MAINTAINANCE is the key. Regular oil changes, fresh fuel, draining the bowl (for extended non-use) will extend the life of any machine.
I'm on my second Snapper walk behind (self propelled) since 1985. This current engine, 7 HP, OHV (considered commercial NOW) is about 11 years old, doesn't burn any oil, leak down test of less than 1% at 100 PSI. The engine's never been opened(except for one valve adjustment check).
During the summer, the yards cut TWICE a week, rest of the year, once a week, 365, so it IS used ore than most..