Excel "apps" that is scalable, maintainable and secure could be built with MOSS (Microsoft Office SharePoint Server) deployment and give the power to end user. Why should we embrace Mashup?

Mashups and SharePoint compliment each other quite well, particularly if your data sources are not just Excel but include SOA services, XML/RSS, SQL databases, etc.  Check out our 10-part blog series on 'Mashups and SharePoint': http://www.jackbe.com/enterprise-mashup/blog/mashing-sharepoint-introduction.  Give us your feedback on it!