The Yamaha apparently goes into non-pure sine wave when it initially sees a high inrush current. I do have an EMS and spoke with PI about it. No mention of voiding warranty (though I have read that warning on their page) just that some Yamaha's have issues.
As far as the motor, I wasn't speaking of displacement as the Honda has the Yammy beat...hence the higher surge rating of the Honda. I was speaking of engine design. Plastic camshaft on the Honda vs push rods on the Yamaha plus the Yamaha is tested to twice the CARB rating of the Hondas. The higher CARB rating means that the Yamaha is built to tighter tolerances and wears better than the Honda. That coupled with the Fuel Shutoff (very important since mine sits a long time between uses) and the fuel gauge and I prefer the Yamaha.