Your top-level reply could be misinterpreted to say that Apple ships an app called "IBM Weather Channel" on phones.

They do not.

Apple ships an app "Weather", which currently uses api.weather.com as the data source.

IBM Weather Channel operates api.weather.com.

TLDR: You're both right: it's Apple Weather, and it requests from IBM directly. https://news.ycombinator.com/item?id=18822350

It would be reasonable to expect that as part of TWC’s contract with Apple, they’re contractually required to keep individual location data private. I wasn’t able to find any concrete evidence of this except for the TWC privacy policy for the Apple TV, which seems to explicitly differ from the normal TWC privacy policy in that it excludes the sale of individual-level data to advertisers. (If I’m reading this correctly.)

https://weather.com/en-US/appletv-privacy/

Standard TWC privacy policy for comparison:

https://weather.com/en-US/twc/privacy-policy#us-how-we-share...

I don’t think that Apple has any technical privacy measures in place here, but I would be deeply surprised if, after all their pro-privacy advertising, they allowed a default app to be (at the contractual level) a giant privacy risk for their customers.