Those versions don't stick around forever, unfortunately. A couple months back I reset my iPhone and it wasn't possible to download the Pebble app any more. My watch still works fine, especially with Rebble cloud services, but the app was just unavailable on the app store. That was the nail in the coffin that got me to switch to Android.
Again, you have to look in the purchased tab of the App Store. This allows you to continue to download apps you downloaded in the past that are no longer available as a new purchase.
