The database deployment toolkit isn't intended to be visual source safe for databases, right?

No.  It can be used this way if you have a package file that is exported you could then re-import it back to the state of the exported file.  But the DDT is designed to be a database design and implementation tool.  There are many benefits past this, such as creating psuedo table structures that are not deployed but allow your BOs to be mapped to these schemas for strong-typing and then use XML as the data source, for example. 

When using the DDT in a normal sense, it will also create all of the SPROCS for INSERTs, UPDATEs, and DELETEs that also support concurrency just by clicking a check box.  These SPROCs tie into the BOs by just setting the CRUD SPROC properties to True.  There is much more than this, but its design and purpose is not to be a source safe for databases.