Exchange Server could be hosted on Macs, but I'd rather see Apple deliver something better than Microsoft and RIM's stuff - and position the iPhone as a better platform than the Blackberry for corporations.
I believe that Apple will eventually spin off a unit for enterprise systems - without the Apple logo on the front panel.
I don't think there's any doubt that Apple has long range plans of that nature. If they don't, Jobs is a bigger fool than his detractors give him credit for.