"The experience on the Office hub [in Windows Phone 7] is better, it's cleaner," Kelly notes. "Because there is a local app, you can download the document and edit it, manipulate it more."

Even in a desktop browser on a Windows computer, Office Web Apps lacks auto-save functionality and the ability to have multiple users simultaneously edit Word and PowerPoint documents. Gartner analyst Matt Cain chalks this up to the capabilities of the browser versions of Office Web Apps to avoid cutting into revenue for Office software licenses.

Kelly says that's not the case.

"It's more just the evolution of where the products are," he said. "If I were to look across the main applications of Office Web Apps, the most mature is Outlook. Outlook Web App has been around for a long time. It's got a really broad set of features that really closely emulate what happens in the Outlook client and that's because we've been working on it longer. If you look at Word, PowerPoint and Excel [in the browser] they're just not as mature."

There may never be full parity between Office Web Apps and the classic version of Office, however. "We don't want to fully replicate the entire experience in the browser because... you can do a lot more when you have that local computing resource and client," he says.