Ungrounded sockets are still very common (just off the top of my head, in Japan, Philippines, Australia, all through Europe, India...). Even as building codes change it takes many decades for the housing tock to upgrade. Even when the code requires upgrades to commercial buildings it rarely will of residential.
If the leakage is harmless (or "harmless) why risk the user buying a product, getting home, and then being unable to use it. The OOBE is terrible and possibly fatal.
This is also why the "international travel kit" for Apple power supplies contains non-grounded plugs.
The authors final and correct point about Apple is fortunately now obsolete as since it was written Apple has switched to standard Type C connectors. On the other hand they no longer ship grounded connectors by default (in the USA at least).