It meshes well with the way Blackberry handles incoming messages (email, IM, etc.) and the Blackberry has a public API to allow 3rd-party access to such incoming messages.

iOS has no such public API, and the various types of incoming messages (email/SMS/IM) are not unified in iOS like they are on BB. It's always been a weak spot on iOS. The iOS 5 notification center improves the situation quite a bit, but there's still no public API to enable a device like this watch.

Most likely that Apple don't provide access to the Bluetooth layer; there's also no bluetooth file transfer apps available.