Re: Xbox 360 / DX10 ?
DX10 from a technical standpoint has a large number of easy of use improvements over dx9c. DX10 has a unified shader architecture, so you don't have to mess with different sets of commands and restrictions between vertex and pixel shaders. It has lower overhead for bulk commands. It has done away with cap bits, ie: you support everything in the specification or your not dx10 compliant. As well as many other improvements. Please note I am not a games developer, I just keep aware what is going on in the industry.
As to the "I need the newest version of this api to make things look better", ultimately that line is and always has been hogwash. Like many other fields of study, once you have been given the basic building blocks anything is possible. Having better refined tools to do the job, simply makes the job easier and more efficient. Which is why there was no visible difference between shader model 2.0 and 3.0, even while the same thing is made easier to develop in the 3.0 model.