Reach4, the Korky solution uses two clips, actually. One is the regular clip, and the other is kind of an "adapter" for the canister flush. The poster could probably rig something up that was creative, of course. But I figure if the plumber has been out a few times, the cost of a couple of the valves, including the special Korky adapter, would be far less than a service call. If they are really creative, they might buy the valve and see if they can just use the tube and clips and save the valves for later, but why not use the great Korky as long as you are at it...
JSK: The Kohler valve is just a Fluidmaster 400A; you could I guess use the hose and clips if they fit.
Most people don't have a flush valve with a canister or the stopper thingy. That's a Kohler thing. American Standard had a different version flush tower for a while, but they dumped it because their version was super-problematic. (In fact, they effectively recalled it, sending out a new type of flush valve to all registered owners. For most owners, replacing a flush valve (as opposed to the fill valve) is a more-involved project than they want to do, because it involves removing the tank, which replacing the fill valve does not. Most toilets still use a version of the "flapper" on the flush valve, which has been around for decades, and it's cheap and generally-reliable and easy to replace.
You can test whether water that is poured into the outer part of the canister indeed goes into the bowl. I would certainly do so before embarking on this. Just take a measuring cup of water and pour it in there and see if water comes out in the bowl. If you're really creative or if it isn't obvious, try it with a small amount of food coloring.
As to "why"? Kohler does a lot of engineering, in my view, that doesn't improve much, but does give them a basis to market that their product is "different". The Korky people probably just figured out that it didn't have to be like that, and engineered a solution. I notice that on the Mansfield toilet, which has a different style flush tower, they just shove the hose into the flush tower, but for the Kohler, they created that little adapter. Now there is (I hope) some smart engineering...
Let us know how it goes.