It's really a demonstration of how Honda's engineers paid attention to details on the SOHC4 engines. Most of their other bikes of the period had chokes that were a solid plate, and the mechanic would have to adjust the stops so the plate did not close 100% when the lever was pulled to choke. On these carbs, with 4 plates to set, Honda seemed to feel that it would be too complicated to try to set all 4 in such cramped spaces, and the carbs are hard to remove (compared to their Twins). On a multi, if one is closed 100% and a few others are open enough to run the engine, and the operator does not realize the choke is on for too long, it will wash down the blocked cylinder with lots of fuel, scoring the walls and rings. Honda was always cautious about these things, to try to reduce warranty charges against them and improve their image with a lower-maintenance bike (at least, while Sochiro was still in charge: this ended with the advent of the CX500 and similar bikes). This won big points with riders who were just get-on-and-ride types, whic was most of the new Honda ridership at the time: these Hondas were the ones that changed motorcycling from forcing you to be a mechanic, to allow you to ride to the office (or school) on a daily basis. The CB750K1 and CB500, in particular, effectively 'won' this battle, and the rest is history.
On comparable "brand X" bikes of the period, the idea caught on after this, and even Twins and Triples started using the spring-loaded flaps. Not cheap, but they do elegantly solve the problem!
