200 hours is roughly 5-6000 miles in mixed use in a car. It is not the hours that are important but rather the way the engine is used. When my last boat was in charter it would run continuously at 2400 for 4-5 hours at a time, totalling 50-60 hours a week. The oil was changed every 3-4 weeks and at 3500 hours when I sold it the engine was running perfectly.
Compare that with typical weekend leisure use where the engine might run for several short periods with the odd longer run, followed by long periods of inactivity. It is the deposits from low load running and incomplete fuel burning that colour the oil and degrade it, not any loss in viscocity (how does you finger and thumb tell you anything except oil is slippery?).
The once a year advice is the best to follow. Hours are almost irrelevant for many people as the typical annual usage tends to be +/- 150 for the "weekend" sailor. If however you do long hours of motoring the 200 hours is appropriate.