As I said on reddit, the name isn't misleading. SQLCompiler is used for generating SQL, and assumes relational database concepts like joins, table aliases, and aggregation.
Now, here comes the surprise: That's exactly what we want to emulate with Django nonrel. It's exactly the feature set we badly want to have. This is the reason why the SQLQuery/SQLCompiler stuff fits so well (though, you're right, we're only using a fraction of SQLCompiler's code, so we could actually implement a simplified base class which is used by both, but we can discuss this later on the django-developers group).