Looking at the Apple World Travel Adapter Kit, I'm guessing the only places where the Mac adapters do come grounded by default are countries that use the UK plug (BS 1363) [1], at least for plugs shipped after 2010 [2]:

https://www.apple.com/us/shop/product/MD837AM/A/apple-world-...

[1] https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets:_Br...

[2] https://support.apple.com/three-prong-ac-wall-plug-adapter

Oh so this is why I feel a slight tingling every time I touch my Mac while it's charging! I was looking for this info for quite some time, thanks