Google has a search index.
Apple has hardware & manufacturing IP.
Also for Apple while I am not sure, but looking at the Android phones there is hardly any feature of Apple which hasn't been covered by some Android phone, so I don't think IP is an issue. It's just that overall quality is much more consistent for Apple across generations that it has built a good brand.
Every company also has a valuation, either through public markets, private markets, or discounted cash flows.
A house cleaning company has a moat of trained cleaners, existing client generation process, goodwill of existing clients, etc. If the value of their discounted cash flows exceed the cost of crossing their moat, they are vulnerable.
The argument is that crossing postman’s moat would cost much less than their private valuation, and their future roadmap is unlikely to build a moat that is significantly harder to cross.
The definition of a moat.