Sometimes, it's not about the gas but how the fuel system is designed.
I almost agree with that. I think it's a combination of both. The only engines (that I own) that have big fouling problems are the 1-cylinder Honda engines. For instance, I have 2 tillers. I can let gas sit in the Briggs engine tiller for 2 years and it runs fine. Same gas in the Honda engine tiller and it's fouled in a couple of months. Same story for the eu2000i generator. When the Honda engine on the tiller is running right, it's one sweet-running engine.