I read on AVS that Pioneer had an extremely inefficient plasma operation, making only one panel at a time, vs other manufacturers that were pumping them out 5 or 9 at a time from one piece of glass.
Furthermore, the word there was that Pioneer is simply licensing their plasma technology and know-how to other panel manufacturers, and that they will continue to research, develop, and market their plasma panels (which will no doubt still be the best).
So they just shut down an extremely inefficient, unprofitable plasma factory and are outsourcing the actual manufacture to other factories instead of making a new one.