you also don't see anything in the ati changelog that happens in the shared code base and benefits both sides. So if AMD tunes fpr a certain opengl app and that influences the linux side too you won't find it in the linux changelog.
Apart from that - what did Phoronix really test? Quake-based stuff, Specviewperf - but there is a lot more stuff.
The general architecture of the ATI cards has been pretty similar since r600 was released, so i'm not surprised that the drivers were already tuned pretty well. The new DX11 features aren't being used in any of these tests, that would be where i would expect driver improvements to show up. The new 6000 series does finally switch to a new architecture, so it would be more interesting to track that and see if the performance picks up there or not. Same has been true of NVidia, using the same architecture for a long time up until a switch occurred with Fermi.
Quoting the nvidia 260.89 linux driver relnotes (from 18.10.2010):
* Increases performance for GeForce GTX 400 Series GPUs in several PC games vs. v258.96 WHQL drivers. The following are examples of some of the most significant improvements measured on Windows 7. Results will vary depending on your GPU and system configuration:
GeForce GTX 480:
+ Up to 10% in StarCraft II (2560x1600 4xAA/16xAF Ultra)
+ Up to 14% in S.T.A.L.K.E.R.: Call of Pripyat (1920x1200 4xAA/16xAF)
+ Up to 16% in S.T.A.L.K.E.R.: Call of Pripyat (SLI – 2560x1600 4xAA/16xAF)
+ Up to 6% in Aliens vs. Predator (SLI – 1920x1200 noAA – Tessellation on)
GeForce GTX 460:
+ Up to 19% in StarCraft II (SLI – 1920x1200 4xAA/16xAF Ultra)
+ Up to 15% in Battlefield Bad Company 2 (SLI – 2560x1600 4xAA/16xAF)
+ Up to 12% in S.T.A.L.K.E.R.: Call of Pripyat (2560x1600 noAA)
+ Up to 9% in Aliens vs. Predator (1680x1050 4xAA/16xAF – Tessellation on)
+ Up to 7% in Metro 2033 (1680x1050 noAA – Tessellation on)
+ Up to 11% in Dirt 2 (SLI – 2560x1600 4xAA/16xAF)
+ Up to 12% in Crysis:Warhead (SLI – 1920x1200 4xAA/16xAF Gamer)
+ Up to 13% in Far Cry 2 (2560x1600 4xAA/16xAF)
+ Up to 12% in H.A.W.X (SLI – 1920x1200 4xAA/16xAF SSAO Very High)
+ Up to 5% in Just Cause 2 (1920x1200 4xAA/16xAF)
+ Up to 22% in Riddick: Assault on Dark Athena (1920x1200 noAA)
+ Up to 5% in 3DMark Vantage (Extreme Preset)
User should use the newer Firepro 8.773.1 and Catalyst 10.12 drivers with the newer Y2010-Y2011 cards. I don't think ATI's current drivers are OpenGL 4.1 compliant (just compatible) yet which help advanced developers push demos and graphics to help sell their software.