Honest question, can't they just ask a chip foundry to make a new batch of the components, with even better miniaturization today? The original used 90nm processes, while the later versions of the console used 45nm, nowadays I think even if they opted for 20-25nm for cost saving, it'd still work fine.
The whole point of bringing out a new generation of hardware is to make it work in much better ways of operation than the last one. By default it is not going to run the older generation of games because it doesn’t work in the same way. Now they could spend a lot of effort in making it able to play the old games and work in the old way, but what is their incentive to do that, compared say in starting work on the next generation or releasing the console earlier?