Jimbo, I read your post on the piano forum
I don't know that there's a concrete answer. I have been intrigued by sustain characteristics in different pianos for a long time now. And what I have found is that it's more a piano to piano issue than a brand to brand issue. There are a number of things structurally that are absolutely necessary for proper sustain. And these things often aren't finished properly in the factory or in the dealership.
One thing I have noticed frequently (even on high end pianos) are bridge pins not properly seated in the bridge. This causes the energy traveling down the string not to cleanly or completely travel through the bridge into the soundboard. I remember one high end piano where we were having trouble getting sustain in the 5th and 6th octaves. After trying to needle the hammer, a massage the felt in different ways, we got a brass drift and seated the bridge pins. Vuala! Suddenly there was clean termination, and the two octaves in question had amazing sustain.
I relate this story to show that sometimes it's not the brand that has or doesn't have sustain. But the individual piano itself. And while some designs might be better suited to a longer sustain, they don't necessarily have it if they haven't been prepped to their full potential.
I would say in general, that performance instruments are designed to have a louder attack, and are meant to cut through more space, while "chamber" instruments are maybe designed to have a bit less attack, and possibly more sustain. Again, this is a BROAD statement, and doesn't mean that one brand necessarily has more default sustain than another