I'm not sure where the 80 hours originated, but I don't know anyone that would actually go that long between pistons on any engine like this one. I would go by what the Aussies are saying for now, as they've been running it the longest.
As far as why this engine is replacing the Yamaha at USPKS, that's pretty easy. Besides all the inconsistency issues with the manufacture of the engine, which requires engines with optimal blow down and the "right' head, case, and cylinder combo to be competitive at the top level, it just doesn't fit with the times anymore. 10, 15, 20 years ago, karters wanted to work on stuff. They wanted to be mechanics and tuners and were willing to take the time to do learn it. Now, most people have sooo many other things that they also want to do, that few want to really learn how to tune an engine properly, or set a clutch up properly, or read EGTs, or set the pop off, or gap a clutch properly. Yes, there are people who still want this experience, and there always will be, but they are in the minority these days. Also, the US and AUS were the last 2 markets for the Yamaha KT100. In Australia, KA has literally replaced the KT in a very short time. The annual production needs for the Yamaha, to meet the US market, can be produced in less than 1 shift at the factory. Yamaha officials have indicated (without coming out and saying it) that its only a matter of time now, until someone pulls the plug on the manufacture.
Somewhere above, someone said that the Yamaha was a very popular club engine. The reality is that Badger and New Castle are the only 2 tracks in the US that have a good Yamaha field. You could throw in Route 66 as well, if you want to cite one more place with a good following for the Yamaha. And while there are thousands of Yamaha engines scattered around the country, WKA's Man Cup series is the only other one that takes them seriously, and they have declined substantially from its heyday in the early to mid 2000s.
I'm not going to refute what was said about the Leopard to MY09 Leopard, to X30 transition, even though I don't completely agree with it, but I will say that the Leopard was probably the longest run for a Tag engine package without any changes, in Tag's short history. It fueled enormous growth in Tag and was remarkably good for the sport. The same could be said about the Yamaha.
Lastly, if the quality and parity of the KA100 is anything like the X30 or MiniSwift stuff that is coming out of IAME these days, it will be a great package, consistent out of the box, and very reliable. Time will tell. In the meantime, enjoy the Yamaha, its still a great, fun engine that provides good close racing at a good value.