Oracle the database isn't really Oracle's main product. They're real product is a bunch of industry specific applications and middleware (and related consulting services) that happens to need a Oracle database to run. So as such they're not really directly competing with SQL server (or postgres or whatever)
That's a good point. I suppose I should have specifically labelled DB2 and SQL Server as competitors to Oracle 10x or whatever their current DBMS version is. :)
That has some big customers -- a large part of Disney's online infrastructure relies on SQL Server, for example.