The US versions of the S III are based on Qualcomm chipsets. I'm no developer, but apparently Qualcomm is much more open to the romming community than Samsung's Exynos team. When I decided to sell my S III, the SGH-I747 build of CM10 was at M1 status. I'm not certain, but I don't think the Exynos-based phones have had an M release yet.

The Verge has some video of the Nexus 4 and 10 in action:
http://www.theverge.com/2012/10/29/3570034/inside-android-building-the-nexus-4-nexus-10-android-4-2

Native widgets on the lockscreen has been a long time coming.