A question came up at Exchange Connections this past week about using a separate name space for the OWA/Web Services/ActiveSync URL than you use for the RPC Client Access area. eg...
Microsoft recommends keeping these separate. While it *does* work if they both point to the same hostname and/or IP address, if they are separate, you reduce the risk of external Outlook clients (Outlook Anywhere / RPC over HTTP) timing out.
Here is the text from TechNet
It's important that the (FQDN) specified in the command be only resolvable internally. If the name is also resolvable externally, these external clients will attempt to connect to the array via a TCP connection instead of HTTPS.
During the session at Connections, I was thinking it was something more complicated than this.