On diesel engines, "they say" that the time to rebuild is really based on gallons of fuel burned more than on engine hours. That is probably true on gasoline engines too, because fuel burn equals work which probably equals wear.
Say your truck gets 10 miles per gallon. After 150000 miles you have burned 15000 gallons. On a boat that burns 40 gallons per hour per engine, that is 375 hours. Not far off from observation for factory engines run in a fast boat. Boost it up and burn 100 gallons per hour, and 100 to 150 hours and the engine needs a rebuild.
That's probably the key issue.
On my boat, I can only run as fast as the ocean allows, so at 750 hours per engine I've still got good compression numbers, no rod knock, everything seems fine, but I burn about 10-15 gallons per hour per engine, so I should see 1000 to 1500 hours. Seems about right.