At least some are. Some are not. Motor manufacturers continue recommending oils suitable to their motor's requirements. Some even have their own oils produced to their particular specifications. Motor performance is enhanced when the same oil is used, mixed the same accurate way with fresh gasoline.
Carb adjustment is minimized, starting made easier.
Bearings, plain, ball or roller, will not perform properly unless clearances are correct, adequate oil is present, surfaces are clean, water and dirt is excluded. Old motors, long out of service, should be dismantled, bearings inspected, and corrections made. As a minimum, fog oil into the crankcase and cylinder, prior to hand turning the crankshaft. The practice of breaking-in uses moderate engine RPM and double the usual oil content to remove minor bearing high points. Useful for new bearing components or adjustments and for long-stored motors.