From the looks of the specs PS4 coding will likely be similar to developing for a PC using opengl, as their current API is really similar to opengl as it is.
Xbox will naturally be more liken to directx (a subset no doubt, with some hardware specific addons).
So really it will be not far off making a game that supports Mac, Linux and Windows. Hopefully that is what will happen meaning it'll take less time for developers to get their games out and start learning to take full advantage of the system (with the hope of it leading back to PC aswell).
The memory part is here nor there, Sony has chosen faster ram, but less of it, while MS has gone with more but slower. It will really come down to transfer rates than the size of the ram. Console devs are already very good at streaming the data they need when they need it.
I remember learning about how they would position the data on their discs for the PSX to get the best loading times. While the bad games that didn't optimize it would have shitty load times.