Check the full post for PowerPoint Web App details
Looking beyond viewing and giving presentations, we knew that people would want to be able to make changes to their presentations from anywhere. Our primary goal is to provide you with a fast and streamlined editing experience, optimized for simple changes on the run. Most importantly, however, we made sure that no matter what changes you make, the fidelity of your document will be preserved.
The latter point is by far the most critical one. The PowerPoint desktop app has been in development for over 20 years. It supports hundreds of features. In the first version of the web app, we knew that we would not be able to support all of them. So we focused on building a foundation for the editing experience that would ensure that even if the web app doesn’t support direct editing of a particular feature, the feature would be perfectly preserved in the document for later editing in the desktop app.