It's not that it will likely make a huge issue, but if we compare the current situation with xbox exclusives being developed for the xsx, xss, and pc all at the same time, to the hypothetical situation of games being developed for the xsx only. The games in the hypothetical situation will likely look and perform better. If a developer can customer tailor their game engine for a single piece of hardware and devote 100% of their optimization time and effort into that single piece of hardware they are going to be able to do more than if they need to develop and optimize for many different potential hardware options.

It's not likely to make a big difference, but a difference would certainly be there.