An official change-log for the legacy version of Catalyst 13.1 has yet to surface, but it looks like this updated legacy driver namely has support for new Linux kernel releases, support for the X.Org Server 1.13.x series, updated distribution packaging scripts, and various bug-fixes.
Being able to run the Catalyst Legacy driver for Radeon HD 2000/3000/4000 series hardware on new Linux distribution releases is a big deal since the open-source Radeon Linux driver often comes up short. The Catalyst driver remains superior when it comes to OpenGL compliance, OpenGL performance, power management, video acceleration, and numerous other features like AA/AF modes, CrossFire, PowerXpress, and much more.
It was in April of last year when Phoronix was first to report AMD would be dropping the HD 2000/3000/4000 series support from its mainline Catalyst driver. The last official update to this Linux legacy driver was Catalyst 12.6 from last summer.
This Catalyst 13.1 Legacy update comes just days after AMD released the Catalyst 13.1 driver as the first official update in a while. This mainline driver update featured X.Org Server 1.13.x support, improved performance for certain games (namely Valve's Source Engine titles), and various fixes.
Download links and other details on today's legacy driver update can be found from this forum thread.