Here is Sony's PR from 2007 in what it means to be supply constrained:
David Karraker from Sony Computer Entertainment contacted us to clarify what the term "supply constrained" actually means. Here's the official explanation.
The industry standard for a product to be considered to be in an "in-stock" position for a store is 30 units per store. This would be the level you would see for a PS2 or Xbox 360. At this level, retailers will feature a product in their weekly advertising circulars. If you are not at this level, retailers can't guarantee consumers will find one if they go into the store and they most likely won't support your product in weekly ads. Although you can indeed find PS3s in stores currently, we are no where near an "in-stock" position.