"But I don't think that would be a great idea," said Miller. "It would pigeon-hole Office [on iOS] if it was only available to Office 365 subscribers."

Miller said there were reasons why Microsoft would, in fact, release Office for iOS, and not tie it to Office 365.

"I have to wonder if the toxicity of the 'Apple tax' would really prevent them [from doing Office for iOS]," Miller said, referring to the 30% cut that Apple takes of all app revenue.

"But I really think they have to do something on iOS," said Miller. "Look at the App Store. Many of the most popular productivity apps are Office emulators. So Microsoft is leaving money on the table that could be theirs."

On the other hand, keeping Office connected to Windows also has benefits, in that Windows is, like Office, a major cash cow for the Redmond, Wash. company. "It's six of one, half-dozen of another," Miller said of the way the decision could go.