Don't know if this applies to small engines (don't see why it wouldn't). I know of some diesel engines used in commercial generator applications that have run over 30,000 hours and are still running. These might be a better comparison than an over the road engine that is typicly only running at about 25-40% load. Marine engines and generator drives usually run at much higher loads. Preoilers supply oil under pressure before the engine starter is engaged. The system works by storing oil under pressure and a solenoid valve is opened just prior to starter engagement.. There are interlocks that engage the starter after oil pressure builds up. Start up is probably the hardest thing an engine endures on a regular basis.
Oil temp is also critical for engines running under a high load. Many marine engines have larger oil pans for increased quantity and this will often reduce temperatures to an acceptable level. It isn't uncommon for a marine engine to have a low coolant temp (because of the large quantaties of coolant available), but also havea high oil temp (due to higher bearing loads). Oil coolers are a must for engines running under very high loads, but they also must be properly designed or low oil temperatures will cause damage as well. Thermostatically controlled oil coolers are the best way to go. They function much like a radiator with a thermostat and will modulate the flow of oil or water to maintain proper oil temperature.
It is also criticly important to allow an engines temperature to stabilize after start up (ie: warm up).
Preoilers and oil-coolers don't come cheap, but they can more than pay for themselves in the right application by increasing the engines life.
Just my .02