The problem with that approach is that these applications are not in fact clients to some server-based application. They are not like ERP and CRM systems, despite Microsoft's and others' attempts to make them so. (One organization I know dropped 90 percent of its Office licenses in favor of Google Docs but had to keep half of its client access licenses due to Microsoft's successful intermingling of client and server technologies.)
Instead, iOS users opt for iWork, Quickoffice, or Documents to Go, not Office. Android users go with Quickoffice or DocsToGo, as do BlackBerry and other mobile operating systems' users. They work with native Office files, so for most organizations, it doesn't really matter that they're not Microsoft apps, just as it doesn't really matter if a user on a PC or Mac runs OpenOffice, iWork, or Google Docs. As long as the tools support the Office capabilities required by your work process, who cares what client is running? IT has cared, but it really shouldn't.
What seems to really perturb IT admins is that these apps come from app stores, where there are no site licenses. And these vendors don't offer enterprise support plans. Welcome to the reality of consumerized IT.
How to manage apps in the era of consumerized IT
These apps -- and more from the Mac, Windows, Chrome, and other emerging app stores -- are purchased by individuals, and most app stores let consumers install them at no additional cost for each device associated to the user ID. There are no site licenses; the Apple app stores, for example, treat businesses pretty much like individuals: Each user gets a license that applies for as many as five of their devices. In the case of a device accessed by multiple users, such as a kiosk iPad or a library Mac, the license appies to all users for that one piece of hardware.
Devices can have apps from multiple accounts. Thus, an iPad could have personal apps downloaded from the user's iTunes Store account, as well as business-provisioned apps downloaded from the business's iTunes Store account or from a network page that provisions a business's internally developed apps to its authorized users.
Note the dichotomy: IT manages internal apps using long-standing techniques, whereas commercial apps are unmanaged.