Well, only because we have to ;)
Seriously though, the vast majority of Edubloggers are MS users and the vast majority of Word docs, presentations and spreadsheets are produced as .doc, .ppt or .xls files.
So, now when you upload or link to any of these documents to Edublogs – your readers will, courtesy of ThinkFree Viewer, be able to simply view (as well as download) the file online in a rather neat fashion.
Check out an example on the announcement.