Good question and explanation.

This is one of those interesting cases where BoL contradicts itself. The SQL 2008 R2 page referred to in the explanation gets in wrong, and the explanation given is in fact incorrect for SQL 2008 R2 (it's correct for SQL 2008, so this looks as if that BoL page didn't get updated correctly for SQL 2008 R2). Resource Governor is also available in Datacenter edition (see Features Supported by the Editions of SQL Server 2008 R2