As I understand it, a subscriber uses a topic url to subscribe to a feed at a hub. The topic url is a feed alias that resolves to a feed that is identified by its feed id. I'm trying to understand why some functionality in the GAE reference implementation is keyed on the topic url rather than on the feed id.
For example: FeedToFetch uses the topic url as an identifying key. If the hub is going to retrieve the newest entries from a given feed why would it want to make the same request again to the same feed via a different topic url?
