Harmonix has announced on its official forums that Keyboard Bundles for Rock Band 3 will not be available for PS3 in North America due to a "regional agreement".
The bundle, which runs $129.99, will only be available for Wii and Xbox 360 in the US. European PS3 owners will still be able to get the Keyboard Bundle for all three systems.
Here's the full statement on the matter:
You may have seen that retailers have taken down the Rock Band 3 keyboard/software bundle pre-orders for PlayStation 3. Unfortunately, this SKU will not be available in the U.S. (including Canada and Mexico) due to the agreement terms for the region. However, Mad Catz and MTV Games are working with those retailers that accepted pre-orders to enable them, if they choose, to honor those pre-orders placed prior to this change as soft bundles (separate discs and keyboards), at pre-order pricing. These retailers will have more details shortly.
Moving forward, the keyboard and Rock Band 3 software will continue to be available as stand-alone products for PlayStation 3 in the US. This does not affect European customers as the Rock Band 3 keyboard/software PS3 bundles will still be available in Europe. The Xbox 360 and Nintendo Wii keyboard/software bundles are still available for pre-order.
In other words, if you pre-ordered the bundle for PS3, you should contact the retailer's customer service department for instructions on what to do next.
Rock Band 3 is out October 26 in the US and October 29 for the rest of the world on DS, PS3, Wii, and Xbox 360.