A phone call, a visit from UPS, a screwdriver, a friend to help me push the thing up my stairs, and the rearrangement of piles of books to get to a wall outlet is exactly the level of effort I consider appropriate to set up a deskside four-server, 64-bit Unix RISC cluster. If I were willing to set aside my requirements for 64 bits and Unix with a U (which I won't), I might let a PC vendor pitch me an alternative. But if that vendor offered to match Apple's configuration at half the price but added just one step to the setup process, dispatched consultants to do God-knows-what to boxes I own, or locked me into their brand, or put a ceiling on my scalability, or gave me two places to call for support depending on what kind of problem I'm having, they'd be out in the street.
I confess that I wouldn't bother taking PC server vendors' calls to begin with; I know exactly what to expect from them, and I know what to expect from Apple. Considering Apple Workgroup Clusters' ideal configurations, services, software, documentation and build quality, all other clusters are officially overpriced and not worth the effort to assemble.