As an administrator of Virtual Machines, I don't entirely mind 32bit builds. If you're making a machine that doesn't need over 4GB of memory, then by using a 32bit OS, all your software consumes less memory when it runs. That's because for 64bit builds, the software keeps 64bit address pointers, not 32bit ones. So they end up eating more memory just to do the same thing.
In the case of Windows 8, it may also have a bit do with backwards compatibility, which is a long-running Microsoft thing. Perhaps some older (but pimp) 32bit server would benefit from an upgrade from an older version of windows? It's a lazy case, but so are a lot of Windows admins.
Finally, I'll offer the idle speculation that Windows 8 is a software project evolved out of a long running series. The 32bit branch may be more of a barnacle than a serious product.
Perhaps the best answer would be people pay for 32bit Windows 8. Whether or not it makes good sense probably doesn't matter that much to the people doing the selling. I wager if no one bought it, it'd vanish pretty fast.
It occurs to me that there may be some low-end x86 cpus intended for mobile applications that aren't 64bit. I have a Windows 8 based tablet with a little Atom chip, my actual chip is 64bit but the machine runs 32bit windows. Perhaps other similar devices have legitimately 32bit chips??