Yes, it does. The CREATE EXTENSION will fail when the extension isn't available, and with contrib typically separately packaged, that *is* going to happen fairly frequently. If that could result in users missing entire tables, that could really suck.

This is just actually installed extensions. That could be inconvenient, but my feeling is that it's likely to be less inconvenient than missing this. pg_dump and pg_restore necessarily just kind of shrug their shoulders here.