People generally associate editing to Office Web Apps, which otherwise provide “browser-based viewing and editing” of Word, Excel, PowerPoint, and OneNote files. That’s understandable: browser-based editing is new for Office, and editing is what makes “information workers” feel productive. Once Office Web Apps got deployed to a SharePoint site, opening a desktop app for viewing a powerpoint slide or word document, excel spreadsheet is a pain. Instead use Word Web App viewer, which let you navigate Office files as breezing fast as you surf the Web.