Here is a quote from tech PowerUp!:
"To better align our strategy with current market opportunities, we've changed the launch plan for R600. We are going to deliver a competitive configuration to market with an extremely attractive combination of performance, features and pricing, targeting a broader market segment in Q2. With the revised strategy, AMD will be better able to capitalize on the broad appeal of 3D graphics and DirectX 10, being driven in part by the growing popularity of Windows Vista™."