Two forces that may play against this: there are a growing number of people browsing from non-Windows devices (OSX, iOS, Android) on which there is no IE option, and for businesses that choose to save money by using Google Apps, it's probably preferable to put their users on Chrome to ensure the best possible compatibility and performance. Yes, IE has tremendous inertia in its favor, but most of the trends seem to be washing the other way.
I think you're right about the growing number of non-desktop browsers forcing IE getting on board, but I've always felt the "web apps" angle was overplayed. I've never worked for a company that migrated to web apps, nor am I personally familiar with anyone who has. I read about them sometimes, but really, what company that employs 500 people is using web apps over enterprise solutions?
Hanging hopes on web apps seems a like a startup echo chamber. Sure, the potential is there for lots of things, especially in the collaboration space, but Google Apps is a Mount Everest away from usurping MS Office.
There are in fact a lot of large organizations in the for-profit, government and education space that have moved over to using web apps at this point. Microsoft Office isn't about to disappear, but it's fairly established now that an organization can exist without buying Office licenses for their employees, especially if they don't have heavy dependencies on Excel.
There are some pretty big organisations that use Google Apps. For example, BSkyB use gmail for customer email accounts, and the University of Cambridge and the University of Sheffield both use Google Apps to some degree for staff/students.
There's a local tech college that uses it for email as well. But that does very little to shake IE's hold in the enterprise. Providing customer or student email is one thing, migrating your staffs away from an MS Office workflow (especially for academics, who's job is publishing), is something wholly different.
I'm not saying that businesses don't use web apps, but counting on web apps to shake IE's dominance in enterprise, at least in the short term, is wishful thinking.
