I own an RC5000 with the light sensor and a Pronto without (blue/green case). I loaded the same CCF into both of them, and looked at them side by side in my dark theater. The screens looked virtually identical.

Sounds more likely that different screen sources/brands is more likely. If that's the case, I'm not surprised at all there is a a difference. I suspect that when Philips went looking for new screens, they simply bought screens that met their minimum tech specs. It wouldn't be too hard to believe that no one at Philips actually sat down and compared the screeens side by side.