If you wouldn't know about some mdb-file, could you connect to any database only from the information given by the snippet
AFAIK, this registry entry simply tells the ODBC driver which specific DB access DLL to load when someone requests to open "SomeName" using ODBC. In essence, this is what your QSqlDatabase calls are doing - you've told it to use ODBC, and you've told it the name of the database, so the ODBC driver is going to out to the registry, look up this information, and open the database if it can.

Any program that uses the Microsoft ODBC driver will go through the same process, whether through Qt's layer, .NET, or some other database access layer. So unless you have code that will read MDB files directly, without going through an ODBC driver layer, you will be following this path too.