Sure there is. For example if you want to use one client on one platform, another client on another. I want not just my subscriptions to be updated on an ongoing basis between two unrelated clients, but play position and play/unplayed to sync.

That said with RSS I just use NetNewsWire which does local crawling of my feeds, and it updates its state via iCloud. But I'd definitely want a web interface if I needed one to access my feeds on a work computer or something.