Of course they're different. A diesel is a much heavier duty beast.

I won't really argue with what you're saying but I think most sailboat diesels suffer much more from infrequent use. Starting, motoring 10 minutes out from the mooring, then shutting down is not a diesels ideal running condition. That combined with shut down six months out of the year for us New Englanders and a salt air environment is what really kills them and should prompt frequent oil changes.

I had a diesel in a pickup truck that again the oil was changed very infrequently and at 300k was still going very strong (well, the engine was anyway).

Plus I speak from just a tad bit of experience having worked in a diesel shop for many years. I've seen more tear downs than you can imagine and in general, it's not the mileage nor the hours, it's the light duty use for something designed to run 24x7x365