>My basic point is that no one single thing can be classified as THE way to define a data/database engine.

Sure there is. A database is:

A collection of accessible data.

If ADO.NET is considered a database it should clear that its collection of data does not persist from session to session without a permanant data store. Because ADO.NET is a temporary data store it doesn't make much sense to call it a database.

But if you need to call it a database to help your argument I don't think anyone will have much luck talking sense in to you.