Seems like the the Sony A55 is indeed using a different sensor from the A33, and that Nikon and Pentax will use that same sensor for their upcoming D7000 and K-5.

At the Pentax stand, marketing chief for the UK Marilyn Dixon proudly showed the K-5. I will admit, this is the camera Sony should have been showing. “We must tell you straight away that this camera uses a Sony sensor”, she said. “Sony make very good sensors”. What of Samsung? She was not sure if they were still selling any K-mount cameras. Pentax might never have used a Samsung sensor, ever, from the impression gained. They were using Sony sensors and Sony were the best