Jim90 :
I can't believe ANY developer would deliberately alienate half the potential customer base
The release of the game is still several months off. It's likely that they are just using those particular CPU and GPU combinations as their optimization targets, and haven't definitively determined what the AMD equivalents for the release version of the game will be yet. As such, it's possible they might update the specifications to include that information closer to launch.
Also, it's probably worth pointing out that AMD has never actually held "half" of the PC market with either their CPUs or GPUs, and their usage has slid a bit more in recent years. Looking at Steam's latest hardware survey, just 21% of Steam users currently have an AMD CPU, while the rest have Intel, and Nvidia also has around 2.5 times the number of GPUs in use. Perhaps AMD's numbers will start to climb again if Ryzen turns out good, though it seems unlikely that they'll near Nvidia or Intel's numbers any time soon.