That’s one of the biggest misperceptions. The ones that depend on the Xserves are the clients who connect to it.
10,000 may be sold per quarter but, the figure that should be looked at is the amount of clients that connect to each Xserve that is sold.
Why is this important? Well in order to support a large deployment of Mac desktops you need Xserves to properly manage them and provide vital services.
Large deployments of Mac desktops depend on the Xserve. Without an Xserve it is difficult to justify purchasing large amounts if Mac desktops which will hurt Apple sales.
Apple needs to develop more complete solutions around the Xserve an properly market them in order to take advantage of this halo effect in the enterprise. So yea many DO depend on the Xserve. Instead if counting Xserve sales count the clients that each Xserve supports.