AMD has sent us a clarification for this matter
: "We will be moving the AMD Radeon HD 2000, AMD Radeon HD 3000, and AMD Radeon HD 4000 Series of products to a new driver support model. We will continue to support the mentioned products in our Catalyst releases, but we're moving their updates to a quarterly basis, whereas our AMD Radeon HD 5000 and later products will continue to see monthly updates. The Quarterly Catalyst releases will focus on resolving application specific issues and critical updates.
The reason for the shift in support policy is largely due to the fact that the AMD Radeon HD 2000, AMD Radeon HD 3000, and AMD Radeon HD 4000 Series have been optimized to their maximum potential from a performance and feature perspective. The 8.97 based driver, released in May 2012 will be the first driver for the AMD Radeon HD 2000, AMD Radeon HD 3000, and AMD Radeon HD 4000 Series under the new support model; it is an extremely stable and robust driver branch for these products and will be the baseline for our quarterly updates.
Our main development and testing efforts will now be focused on the AMD Radeon HD 5000 and later products. This is the best use of our resources, as the AMD Radeon HD 5000, AMD Radeon HD 6000, AMD Radeon HD 7000, and future products have the greatest potential for further performance and feature enhancements.
Also with regards to Windows 8 support for the AMD Radeon HD 2000, 3000, 4000 Series of products; the In-the-box AMD Graphics driver that ships with Windows 8 will include support for the AMD Radeon HD 2000, 3000, and 4000 Series, and it will support the WDDM 1.1 driver level features. The AMD Catalyst driver for Windows 8 will only include support for WDDM 1.2 support products (AMD Radeon HD 5000 and later)."