The ability to edit Office Docs in Chrome OS comes as an answer to compatibility challenge presented by Microsoft's Office Mobile, while filling-in the gap on Google Apps incompatibility problems.
Google's attempt in deploying QuickOffice within a browser has long been rumored, and now has eventually found its way on Chrome OS. The company has labored to bring the compatibility aspect along with the functionality of Google Apps.
Google's QuickOffice, however, does not present any threat to Microsoft's Office Suite, because its functionality cannot yet match the later. But given the fact that it's running on the unstable Dev channel of Chrome OS means the feature has not been made available for the public, hence not fully ready.
Eventually, within the coming months will see the arrival of the feature to the stable channel. Before then, if you would like to give the new feature a spin, you'll need to get a Chromebook while ensuring its running version 29.0.1547.2 or later.