Everyone seems to think it is so easy to explain why productivity can rise when employment falls. It is -- IF labor demand is stable. The observation that "marginally" productive workers are the first fired is exactly what it means to move ALONG the labor demand curve.
The real question is how do you modify your prediction for the previous severe recessions -- when productivity FELL?! Here's what I say: that's when demand shifted more than supply.
This is why I have spent a whole week asking: why does the labor demand curve shift so little in this recession, and so much in previous (severe) ones?