Actually, the enterprise segment is more profitable than the consumer gear (Intel and system vendors other than Apple - much better margins per system, combined with higher volume sales for large customers).
For example, if you recall the recent news about HP considering selling off part of their business, it was the Personal Systems Group (PSG) that was potentially on the auction block. Not the Enterprise System Group (ESG), which is due to it's profitability vs. consumer gear (there's more than just systems in the enterprise segment as well; there's other hardware and software offered that allow a customized
integrated solution for clients).
Consider this:
A consumer user will go out and buy one system at a time, while enterprise customers order more, much more in a number of cases. Particularly the larger ones, which are far more likely to order thousands of systems per quarter when an upgrade cycle is due (think Fortune 500 and larger). And there's all SMB's as well... not as many systems, but they still order more than typical consumer users do.
Combine both the higher system sales volume per customer, and the fact that each of these systems contain more profit per system than their consumer oriented products, it's no real surprise that the enterprise segment really is more profitable.
Apple just never got serious in this market. Now I'm not sure if they just screwed up, or decided early on that the ROI wasn't going to be good enough for their tastes (take to long to see their idea of suitable margins), but the XServe languished as a result, regardless of the specifics. Since they can't really compete in this section, they've focused in another direction that has high margins/ROI, which is the high-end consumer market, and particularly the devices as of late.