Xcelsius Engage Server and Sharepoint

Hi

I'm looking at the product comparing on http://www.sap.com/solutions/sapbusinessobjects/sme/xcelsius/productcomparison/index.epx and can see that if we need Sharepoint integration we need the Xcelsius Engage Server and install an integration kit on both the Xcelsius server and Sharepoint Server.

However I don't get why Xcelsius have to be server-side when it have the data integration features. E.g. when it integrate to Sharepoint this is done by a 'special Xcelsius' webpart which import a swf. I guess that the swf is fysical stored on the Sharepoint server and if it connect to backend data using a webservice this is running on the BOE. I don't see where the Xcelsius server comes in the picture. I might be that I miss some basic understanding of the processflow ( surely I am 😊), so I'll be grateful if anyone can explain me why Xcelsius need to serverside when it integrate to portals.

Thanks,

John