I personally think this is just a 1.6c instead of a completely new version. Why? It makes no sense for M$ to put out a new Motherboard, when they are phasing out the old Xbox for the 360, unless they can get sued for something that could go wrong with the old Xbox.... The power supply! While I'm not sure if the 1.6's PSU can go bad (forget), with the Anti-trust lawsuit in Europe, M$ probably wants to cover every possible thing that could go wrong. Thus, with the power supply change, the chip must have to get power from somewhere else, and instead of just telling people the point, they will milk this for as much as possible, and only give people the "fix" with their SmartXX.
A lawsuit is the only thing that could motivate them to change, especially when they need to get the 360 done.
Take care,
TheTK421