Outlook is a part of Office. Also, I’m not sure ‘vertical integration’ is the only way to succeed at business. Google is trying to do that here - with a fast-changing landscape, one would want to use the best downstream provider.
I was trying to think of user-perceived surfaces. I'd expect most Outlook.com users are not office users, as they originated as Hotmail or MSN users.
One would want to use the "best" downstream provider, but part of being best is the cost. Would you accept a chip that's 30% slower and 80% cheaper? Yeah probably, especially if you're serving at scale to non-paying traffic. I don't think Google/Amazon/MS need to make chips as fast as Nvidia, or as scalable, as long as they work out for serving costs at scale and have the enabling technology (mostly about sufficient memory).
