IndexedDB Versions

I am wondering why versions are required in the IndexedDB specification. If
I'm reading the specification correctly if you want to add or remove
objects or idecies then you need to increment your database version number.
Perhaps I'm wrong, but this seems to be rather arbitrary. It makes more
sense to me that there would be no version at all, but there would be a way
to programmatically determine if an object store exists or if an index
exists.

Thank you,
Mahon