I never understood why Apple even bothered with the X-Serve and it makes perfect sense for Apple to shed a product line that doesn't add to the company's overall value chain. Apple is a provider of client products. Apple is a consumer electronics company that also provides content. That's where their focus needs to be.
Apple's internal IT and data center needs are provided by a hodge-podge of IBM/AIX, Sun/Solaris, Red Hat Linux, customized UNIX, Oracle, SAP, even Windows, etc. These are systems that would cost tens of millions of dollars. Just do a search of Apple's job listings that Apple is trying to fill on the IT side and there is hardly any mention of the X-Serve or the Mac OS X Server at all. It's mainly heavy duty enterprise backend stuff dominated by IBM, Linux, SAP and Oracle/Sun.
Apple's push into the enterprise is for the adoption of the iPhone, iPad and, to a degree, Macs, but it's mainly about mobile. Apple hired Unisys to help large enterprises integrate the mobile devices into their IT infrastructure. Again, it's about the client side, not the server backend. Apple is not going to compete with the likes IBM, HP, Fujitsu, NEC, Dell and Sun, etc on this end. What is the point? It's just not Apple's area of expertise.
What value would Apple add on the server side when cheap generic Wintel or Linux machines can do much more for much less? Industrial design, the look and feel, the user experience and the ecosystem mean nothing in this space. Let's remember what happened to Sun. The server machines have become commoditized. That's why the likes of IBM, HP and Dell are focusing on software, storage, networking equipment, and services like consultation and systems integration. They can't grow or rely on the increasingly thin margins of the server hardware. And unlike on the consumer client side of things, Apple has absolutely nothing to add to the value chain there.