There are many benefits to shrinking, but you have to do a case study to see if it is worth it.
costs:
R&D
Retooling the assembly lines
savings:
shipping
boxing/case/component costs
warehouse space
It also gets more consumer interest.
If the savings outweigh the costs in any reasonable amount of production units and you have enough stock produced to hold you over on a retooling of the assembly lines, then it makes sense to do it. The end of the generation makes more sense to make this move, as you probably have good stock left over of the old model as sales are starting to decrease and the assembly lines haven't been shut off yet.
Since the PS3 and X360 are larger and heavier than previous generations, it makes sense that the potential savings are higher, but I don't think it is enough to warrant slim model so soon. However, gamers just like to speculate and want a small console anyways.








