I think IBM shovelled off the PPC 4xx property (for $127 million I believe) in order to concentrate on a few big clients (Nintendo, MS, Sony) and spend more resources on their technologies..
Seeing as each company is getting a different flavor of their POWER architecture it seems unlikely that they're spread too thin. They just gave every company what they wanted. You can spend development dollars on making a massive workhorse of a CPU that costs you an arm and a leg to fabricate, or you can throw them at a more light and lean design, with smaller die space and higher yields.