Is OPENXML the only way to work with Office documents server side in SharePoint 2010?

I assumed that there would be server side API to open an Excel document from a document library, do some processing and commit that file back to a library.

I know that there are Excel Web Services, but not really what I need (plus thats an Enterprise only feature, we are Stan开发者_如何学编程dard here).

For example, something like this? http://blogs.msdn.com/b/ericwhite/archive/2010/03/24/modifying-an-open-xml-document-in-a-sharepoint-document-library.aspx

I've had a lot of success using NPOI for manipulating Excel documents.