presumably they're storing the raw, uncompressed video? at the same time, I would imagine storing a couple extra terabytes of data isn't a significant cost in the scheme of a production.
For example, most open source library projects that you include in a project don't change from build to build, but ant dutifully recompiles them each time instead of caching the output until the files in that project are changed or I manually clean the build output.
Makes me wish Android could request some permissions at runtime.
It's painful to have a bunch of permissions in the manifest that aren't used by 100% of users, but 100% of them have to allow them if they want to install the app.