Why does it matter who gets credit? The only thing that concerns shareholders is making a return on their investments. Offering Office for iPad is a great plan to make money, since it will encourage more Office 365 subscriptions. This is a win for shareholders, no matter whose idea it happened to be.
I suppose that, in the grand scheme of things, it doesn't matter. And, really, this is just one more example of something major that I see as a problem in the tech media. Whether the tech media gives credit for something or not depends on whether or not they like them specifically.