So no global warranty, but also no global repair or replacement of parts with official parts even when you are willing to pay for it.
[1] I was in the Philippines and I was getting off a boat in shallow sea water. My phone was in the bottom pocket of my beach shorts, and I walked through the sea water for maybe two to three metres distance up to waist height depth. This should have been ok for the depth I went.
Their suspicion was that the outer seal had failed (even though it had always been in a case).
You were lucky and got it replaced under goodwill, as iPhone X has an IP67 rating[1] and specific about sea/salt water damage -- the kind you have described. Back home, you would have had to deal with a lot of grief[2].
[1] https://www.iphonehacks.com/2018/04/iphone-x-ip-67-water-res...
I think I was definitely lucky yeah!
There isn't much arbitrage for new Apple products: if anything, iPhones are more expensive in other countries, especially LEDC countries due to import tariffs (e.g. Brazil and India) and VAT.
That said, I can understand phone companies, in general, not having worldwide warranties because localized phones will have different radio hardware (well, prior to LTE...).
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I just found Apple's current warranty doc for the iPhone, iPad, and iPod and it does mention international coverage ( https://www.apple.com/legal/warranty/products/ios-warranty-d... ). It would be bad PR for Apple if tourists and businesspeople in foreign countries couldn't get their phones repaired on holiday or during a critical business trip.