Will be interesting to see who wins this race. Not sure if you caught this from WWDC but Apple announced iWork in the cloud and it can be found at beta.icloud.com.
Around the launch of iCloud Steve Jobs made mention that iCloud is the future of Apple. This vision is slowly starting to come to light. iCloud is not a Dropbox clone, its a cloud operating system. Its funny, right around the time Apple launched iCloud.com I KNEW they were going to do this.
Pages (Word), Numbers (Excel), and Keynote (PowerPoint), all written in HTML5. Each app syncs its core data with iCloud so if you switch to a local desktop or mobile version of the software everything is the same. What Apple is doing here is only a first step. I fully expect an App store along with a developer SDK to come out in the future.
Why would developers write native HTML5 apps within Apples walled garden? Deep integration with iOS and OS X desktop products. Integrations that would be impossible any other way.
What surprised me the most however, is that Apple announced all of these iCloud apps will function on other operating systems in Internet Explorer or Google Chrome on Windows or Linux.