This is not just an issue with Outlook, I don't know why many services do a numerical count so you can be quickly aware of the number of items you have.

For example, on my router at home, I wish there is a numerical list of the MAC IDs I have allowed on my router access list. There are many places where a numerical count would have come in handy, so I can quickly determine changes. I don't know why more applications / places have a numerical list feature.