Correct. Many of them do, primarily for GPS elevation and indoor altitude related reasons. The thing is, a massive, dense network is needed for weather forecast

Correct. Many of them do, primarily for GPS elevation and indoor altitude related reasons. The thing is, a massive, dense network is needed for weather forecasting, as that solution requires hundreds of millions of barometers. So the barometer in the iPhone isn't crazy news on an individual level...but it dramatically increases the availability of live atmosphere data.