They are named the same, but they aren't the same. There is a role called db_datareader and there is a schema called db_datareader. This is a holdover from the SQL Server 2000 days when the users in a database were also effectively schemas if they owned any objects. You couldn't separate the two.
Treat the roles as roles and the schemas as schemas. I would recommend not using these pre-generated schemas, however.
K. Brian Kelley