I am surprised you did not include iCloud in the public cloud options. It is the native cloud environment for the iPad as well as tightly integrated with OS X (and more so in Mountain Lion), as well as available for Windows -- which I guess you presume most businesses run. I would prefer iCloud over any of the other 'free' cloud storage, any time.
Also, it seems that Pogoplug is an public cloud offering as well. Same for Oxygen. Desktop Connect is also not a cloud application but rather remote desktop access application. This leaves only Polkast as private cloud in your list.
What is 'business document files'? If these are the typical PDF, Office documents etc, there are native iPad applications that will view and even edit these. If these are some other, proprietary for your business formats, then you either need remote desktop or write your own iPad application.
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