You can. XServe is essentially a vanity purchase, and no company in their right mind would buy them. They're about twice as expensive as the same box from Dell.
Apple needs some way to differentiate themselves then. If Grand Central is ridiculously better (just for example) than anything the competition have, then it might be work it. If you just want to run JBoss or something tho', buy a stack of beige boxes and just throw them away when they break,
Apple's enterprise "goal": be able to sell a compelling "smart enterprise" toolkit that "just works", and is a near-
complete top-to-bottom solution.
What this would wind up looking like: all employees have company-issued iphones (or iphone-like devices, if more form factors become available), company-issued apple laptops, and there's a couple xserves in a closet somewhere.
The xserves give the company integrated calendaring-and-task-management that just works, along with a platform for running whatever internal webapps, file serving, and related tasks.
The iphones are smoothly synced up to the company calendar, and possibly are running some in-house applications (eg: for a logistics company, the data-entry software the delivery guys use to note when and where stuff got delivered). Because these iphones are company-issued the company has some backdoors to the iphone's drm layer; this adds a layer of security to the devices in the event that an employee loses the phone and/or attempts to go rogue.
The laptops play nice with everything else.
Currently you can cobble together an equivalently-functional system with a combination of exchange, blackberries or windows mobile devices, and a lot of custom development and system integration; this is very doable once you're large enough to have a dedicated IT staff, but is often out of reach for small-or-midsize businesses.
Apple would like to be able to make this a turnkey system: you pays your money, and get an integrated phone/email/calendaring/collaboration environment; plug it in, set it up, and you're done, and no more sourcing your combined it-and-telecom services from many different vendors.
Target customers would include schools, medical and professional offices, and anyplace else where there's a huge gain from more-efficient scheduling and communications but not necessarily a lot of ability to develop in-house grade-A technical staff; fortune-500 types might also benefit, but wouldn't be the direct target.
Apple's biggest holdup here is email: they've licensed a lot of what you need to work with exchange, but they don't currently offer any way to run exchange yourself, and they don't have a competing product...ical is nice, but it's not exchange.
Until the email-server issue is sorted out, I can't see apple officially trying to enter this market.
It's worth noting: even in the event this succeeds, the xserve is never going to make sense as a beige-box replacement; it'd just be a major component of an integrated vertical solution.
