Gives people the same option if they went for mantle though.
With mantle you have a choice of having a smoother and potentially higher performing game on AMD cards and having to stick with DX on Nvidia and potentially not have as smooth or high performing experience.
With gameworks you can either have a few extra graphical features on Nvidia cards or not have them on a AMD card.
Either way I would rather have neither of them and have a engine that is designed to work smoothly on both AMD and Nvidia, cards than a engine tweaked to work better on one card or look better on the other.