PowerPivot in excel (what you call standalone) is recreating the excel chaos we had 10 years ago and are still dealing with today i.e. localised databases wiht expertise on what they mean in one persons head.
When you publish a PowerPivot to Sharepoint with PowerPivot installed it is shareable with your team. It can be managed via the PowerPivot mangement dashboard in SharePoint administration, and the user can schedule for the data to be regularly refreshed from the sources the data came from. Finally you can consume the data in the PowerPivot in Reporting Services and Performance Point and share the data in reports and scorecards. thus PowerPivot for Sharepoint is essentially a lightweight self service verison of analysis services (which you can test by copying the part of the url that points to the powerpivot.xlsx file and connecting to it in sql server management studio (as an analysis services connection)
I have a fun video on YouTube http://www.youtube.com/watch?v=Y3s3wOCXTz8
if you want to know more