But it’s best not to overthink this. Office for iPad would sell a lot of iPads. That’s the bottom line.
I look at Office for iPad like I look at Exchange support for Mac, iPhone, and iPad. Apple would prefer that it didn’t have to build support for it, but the Exchange environment is so huge in business that its hard to ignore. Yes, the iPad can survive much easier without Office than it can without Exchange support, but I only think it helps sell more iPads (and potentially a nice 30% of whatever Microsoft sells Office for).
Imagine if Office 2013 for the Mac was in the App store and it included iCloud syncing with Office on the iPad? That’s huge for education and business.