The rationale is if something is not "advertised" as water resistant, any small signs of corrosion will be attributed to water damage and warranty won't be accepted for any reason.
The same as keyboard malfunctions were attributed to hard typing, breadcrumbs and so on.
I do admit that one of the previous photos about an additional membrane that covers the holes puts things more into perspective. It's just not clear if it actually plastic or just another mesh to protect the drivers from dust (like in desktop speakers).
I hope iFixIt will clarify this ASAP.
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