It seems to me that, if Apple so desired, they could make a fair bit of money selling a 'private iCloud' service to companies looking to incorporate iPhones and iPads into their infrastructure in a big way. In the same way companies can set up their own BES server to provide in-house management of their data, the ability to set up an in-house iCloud server, to back up their employees' documents, data, settings, etc., as well as 'find my iPhone', distribute out custom books (e.g. corporate training documents, procedures, forms, manuals, etc.), and in-house apps, could be very appealing to a lot of companies.
I'm sure Apple's considered it, but I doubt they see enough of a market in the product to bother packaging it up and selling it. It's obvious that they're not incredibly interested in the server or high-end enterprise market, and they're perfectly content to let their Activesync integration carry them for now.
Apple have been going at a clip these past few years creating, scaling and tweaking a few massive products - ipods, itunes, iphone & ipads while outpacing competition with macs and still carrying a few fizzles (apple servers, apple tv...) and a few lower visibility but fairly important products (iwork, ilife..).
I think they just don't have the capacity to do more big things right now. When/if iOS gets put on medium heat like OSX is/was, then maybe we they'll try this. It's not really much harm waiting a few years to see if/how some of the newer Apple stuff (iOS, icloud) and its competition gets used by large companies.
I'm sure Apple's considered it, but I doubt they see enough of a market in the product to bother packaging it up and selling it. It's obvious that they're not incredibly interested in the server or high-end enterprise market, and they're perfectly content to let their Activesync integration carry them for now.