AMD Mantle, in theory, isn't designed to port old consoles games to the PC. It's designed to port new console games to the PC. This increases the consumer base instead of isolating them between those who have high-performing computer rigs, consoles, and low performing computer rigs. Remember, AMD won the Console Wars. So any Console game they place on the PS4, will more than likely be ported to the PC. This results in more revenue returns because more people can play the game without deciding to purchase a new PS4 or XBone. If demand goes up, the Game Developers will produce more copies to make more money, and invest in future games. Part of the reason why the Cellphone and Tablet market has become so significant is the fact that the Cellphone isn't just a cellphone. It's a cellphone, computer, web browser, GPS unit, camera, digital music player, etc... So it's basically combining the markets of other products into one. Ask yourself. Would you purchase a $1200 dollar SLR Camera with 28.8 mega pixels, or would you purchase a cellphone with a digital camera that has 24.0 mega pixels, same zoom as the SLR, including the cell phone, web browser, etc for only $599? Practical choice, you'd choose the cell phone because it does about the same as the SLR camera, and it has more features, for a little less than half the cost. Same ideology goes for AMD Mantle in one perspective. You can buy the same games for the PS4, and play them on the PC... You don't need to spend another $399.99 for the PS4 just to play them... Consumers don't need to spend $2000 for a top of the line Alienware Computer just to play awesome-sauce PC Games like BF4 when they can do it on the PS4...
I suspect that XBone will be better at streaming games through Cloud...