Excel on browser ( Excel Web App ), Powerpivot and Sharepoint

I was reading Andrew Fryer's Blog on a post regarding Powerpivot management and the first sentence said that "The most important thing about PowerPivot is the ability to share users analysis into SharePoint so that these other users can slice and data form within a browser."

For those who are not aware, Microsoft Office 2010 has come out with a new neat feature that can be thought of as a NANO version of Microsoft Sharepoint, but it brings to the table a very important functionality. This application is called Excel Web App and is a light-weight Excel client that allows to collaborate working on excel workbooks more or less like Sharepoint using a browser. Keep in view, that multiple users can work together on it, but it should not go under assumption that it would have all features that are available while working on worksheets that are hosted on Sharepoint. Obviously, it won't have those features as they are not Excel but Sharepoint features.

The point that I am trying to make is that, if Powerpivot can be used in conjunction with Excel Web App, need of Sharepoint can reduced helping small scale organizations to still have the minimal required features like simultaneous collaboration and analysis capability of Powerpivot. I don't think powerpivot is supported from this application as of this draft, as I read on the Excel Webapp overview post comments that "Excel Web App cannot run add-ins built for the Excel client app". Thru the course of evolution or thru some workaround, it can be effectively used to replace Sharepoint if just collaboration of Excel worksheets is the most used feature on Sharepoint for your organization which would reduce huge costs.

I am NO expert at Excel Web App but having worked with Excel Services on Sharepoint Server and having read the post on Excel Web App overview (do not miss reading the comments on this post) and this post on Collaborative editing using Excel Web app from Excel Team, I am very sure of the point that I am trying to make is possible and a practitioner or Excel team can confirm the same. I am happy to learn if there's anyone out there who have got different views on the same. I have posted question on the same to Excel Team, do check out the Excel Web App overview post for the answer from Excel Team.