Moss, most of the examples you give involve older engines. I fully agree that older engines don't seem to be as bothered with E10 (hence, the example of my father's tiller). In general, I also find Kohler engines less susceptible and Honda the worst. I have a 13 HP Honda carb that's been cleaned twice in two years. Lately, I've become MUCH more diligent about adding fuel treatment and draining the fuel tanks. In the summer, I run through 30 gallons of gas every two weeks on small engines alone. So, it's a pain to ensure every engine has treated fuel unless I start treating in August (some engines are run infrequently). I also bought a very nice powered kit specifically designed to drain fuel tanks. Works great. Once the tank is drained, I start the engine and run until it quits (to pull the fuel out of the fuel bowl...if it doesn't already have a convenient drain).
BTW, for those who don't know, most better quality 2 cycle oil already has a fuel stabilized added. So, you usually don't have to worry as much about 2 cycle fuel.
There is one bright side to this issue. It's pretty easy to find a nearly new product someone is selling because "it doesn't run right." I've picked up several tools this way for cheap money. A little carb work and it's good as new...until next time.