Vibration next to the touch pad

I notice a vibration next to the touchpad on the aluminium surfaces on my Macbook Air (early 2015). I went through a few discussions around. This seems to happen only when I use the Two pin adaptor directly fixed to the mains plug ie. without grounding. On attaching the longer cord with the 3 Pin Plug, the vibrations clearly vanish.

My question hence to Apple is "Why does Apple even provide an option to use a 2 -Pin plug directly without earthing. World over, it is known that grounding is absolutely essential to prevent equipment damage from static leakage? Does Apple recommend usage of such electrostatic sensitive devices be used with "zero" grounding ? and give rise to such issues and concerns ?