A lot of big customers sign multi-year license agreements for Microsoft software. Once they're locked into these agreements, Microsoft can tweak the rules with each new version of its software. These rule changes can stall competitors, push new products, and gradually raise prices.
Customers go along with the tweaks because it's still cheaper and less disruptive than replacing all their Microsoft software, or buying it without the standing license.
Here's what's going on in this case.
Companies can use a technology called "desktop virtualization" to give iPads (or other devices) access to Windows apps. Basically, the customer creates a virtual Windows desktop living on a server, then uses technology from Citrix, VMWare, or another provider to let other devices tap into this Windows desktop remotely. (Desktop virtualization can have other benefits as well, like reducing the management overhead for regular PCs.)
For iPad users, it looks like they're using a Windows desktop. But as soon as they're done with the session, it goes back to being an iPad.
Microsoft has always charged each accessing device a fee -- it's basically like paying for Windows. You can't get away with using Windows without paying Microsoft.
But CRN reports that with Windows 8, Microsoft is adding an ADDITIONAL fee, a license called the Companion Device License, or CDL.
The catch: it only applies to iPads or other non-Windows tablets.
If you use a Windows PC, or Windows RT tablet, there's no extra charge.