But are we not seeing some engines rated for both commercial and recreational applications? What is going on when that happens? Some fuel pump change or just lower WOT RPM spec to achieve commercial. I mean, I dunno, just asking.
Typically it's a difference in fueling curve and governed RPM. But on some engines, there are upgrades to the internal hard parts on the high output variants. As an example, the Cummins QSB 5.9 is one engine up to 380hp, then the 425, 440, and 480hp variants have some internal upgrades. The newer QSB 6.7 is the same engine across all power ratings, however, right up to 550hp.
Basically, on the lower output / higher duty cycle variants, they reduce max RPM a bit, reduce max power output and adjust the fueling curve to reach a point where it's durable enough in the expected usage.
Looking at the Cummins QSM11, they offer a bunch of ratings:
300hp / 1800 RPM - Continuous
355hp / 1800 RPM - Continuous
405hp / 1800 RPM - Continuous
405hp / 2100 RPM - Heavy Duty
455hp / 2100 RPM - Medium Continuous
610hp / 2300 RPM - Intermittent Duty
670hp / 2300 RPM - High Output
715hp / 2500 RPM - High Output
The Cummins rating descriptions can be found here:
https://www.cummins.com/engines/marine-ratings