You have a small detail that has been written incorrectly. ATi's internal nomenclature is XL>XLE>Pro>XT>XTX. While the Pro suffix isn't used this generation, the XT and XTX are. The XLE is NOT more potent than the XT. The XT means "Extreme" and XTX means "Extreme Extra".
The "Radeon Graphics Division" is only called that as a marketing term. Internally, AMD still refers to it as ATi and that is shown in the driver source code and in the model number nomenclature. It goes back FAR with part numbers like the HD 2900 XT, X1950 XTX, Radeon 6900 Pro, Rage XL and even the VGA Wonder XL.
These designations are not only older than the Radeon name itself, they are older than the Rage name. They have been used internally by ATi since the dawn of their existence and first publicly used as a differentiation suffix on the ATi VGA Wonder XL.