Absolutely agree. OpenGL, SDL, Cairo, all are great and useful for their own purposes, with rather small overlap between then. A single uniform API for graphics is practically impossible, so why bother? To attract beginners?
Graphics has very limited usage without full GUI. I can think of only games and chart-rendering applications (or similar) that don't really need GUI. But games require some means for windows-handling (like GLUT in OpenGL). And "chart-rendering" require output routines to produce PDF/PS/SVG/PNG.. In any case, you need quite a lot of auxiliary IO functions to really do anything useful. So, how much of thes auxiliary stuff will be included in the standard library?
Also, if they plan to implement output with both DirectX and OpenGL, there is quite a lot of work to ensure that everything works on computers with GPU, without GPU, with ancient GPU, on Windows, Linux, OSX and actually looks roughly the same. This is not easy, if you want to do it efficiently.
For game development, beginners choose Flash game engines, or GameMaker, or something like that. I doubt that C++ can work better for them, even with Cairo built in.
The standard library will always have limitations, so you will need to use external libraries at some point anyway. And a transition to an external library can be difficult, if the standard library is already used extensively.
Yes, probably, humongous standard library is good for cross-platform development, but it must be implemented first. And again, external libraries are sometimes necessary anyway. Also some UI libraries are already cross-platform, like Qt, btw.