Microsoft recently announced that it is accelerating its development on Office Web Apps. In the past, Microsoft's strategy for offering Office (Word, Excel, PowerPoint) functionality through a browser seemed to be "just do the minimum." Now, Microsoft appears to have embraced the idea that offering Office functionality through a web browser--any web browser--actually expands its available market opportunity.
Not only is Microsoft expanding the feature set for Office Web Apps (such as support for document co-authoring in Word Web App), it is planning support for Android as well. Having already expanded support for iOS, this means Microsoft is targeting all relevant device platforms, not just Windows.
As I said in a recent talk on this subject, Microsoft's "web first" strategy underscores its "no Plan B" strategy when it comes to making Office, Exchange and other services available as cloud-based services.