Personally I think they may be saying what they are about how long you should run the engines because of the warranty they offer, if an engine goes bad they probably ask the customer about how long they thin the engine had been running when it failed and if the unknowing customer was to say that they had been out riding their 2 smoker powered bike for a couple hours, they may be told that is what killed it since they recommend they not be riding over 30 minutes at a time.
May be a way to get around the 6 month warranty in that case...
Just a thought off the top of my head about it since that is the first I have ever heard of that myself
Hmm I've got an older engine that has made several 25 mile one way trips at wide open throttle the most of the way and that engine has horrible balance.
maybe, I need to tell the lawn care people around here to time how long they run the weed wackers and chainsaws also...LOL!