There's Windows SharePoint Services (WSS) and then there is Microsoft Office SharePoint Server (MOSS). MOSS considerably more expensive than WSS (which ships as part of Microsoft Server licensing).
My question is: what does MOSS do that makes it worth the extra cost?
..and does Microsoft Search Server not compete with the Business Data Cache (BDC)?
Edit: The feature comparision page is helpful in illustrating the numerous features that MOSS has and WSS does not. By the looks of it, most of MOSS's feature set is Enterprise oriented.
How would you describe the differences (or additional benefits) of MOSS over WSS in a couple of sentences? In essence, what are the "big ticket" items in MOSS (and not in WSS)?
About WSS vs MOSS:
About Search Server and BDC: They do not compete.
Search Server is the MOSS search engine striped out. So you have only search functionalities (you can index SharePoint, WebSite, FileSystem).
The BDC (Business Data Catalog) allows you to view an external business data source, such as a SQL database (not necessarily SQL Server, it can be Oracle, MySQL....) or webservices. You'll be able to view data in your portal, and integrate this data to any of your list. The BDC also allows you to index this content source if you have SharePoint Enterprise Edition.