Recently, AMD committed to releasing technical documents for their GPUs in order to assist open-source software developers to write better 2D and 3D graphics drivers. AMD actually followed through with that committment as well, and you can find the technical documentation here, if you're interested. Thanks AMD!
Although AMD will continue to release binary-x86* Linux drivers, the release of their chipset documentation (actually for R300 R500 and R600 series), is intended to improve the 'out-of-the-box' experience for PC users.
AMDs chips are entirely x86, from what I can tell, although I think i remember a rumor that they licensed some of their graphics technology to Apple for the chips that went into the iPhone, iPad, and iPod Touch. Aside from that AMD has no (publicly visible) vested interest in having graphics drivers that are architecture independent.
On the other hand, NVidia actually purchased an ARM License and produces their own Cortex-A8 and Cortex-A9 silicon with integrated NVidia graphics (Tegra, Tegra2), so they have both an x86 and an ARM presence now. Not only that, but NVidia continues to be the sole surviving GPU company, since AMD bought out ATI.
However, NVidia seems to be encountering production delays trying to get (Linux-based?) Tegra2 products to market. I can only assume that they aren't having silicon issues, so it really must be an issue getting the hardware to work well. They have opened up their Tegra2 site to Linux developers, offering a development board, source code, and binaries. However, I'm really left wondering if they could also benefit from disclosing some documentation of their graphics cores and perhaps the Tegra2 TRM, so that the next generation of NVidia-powered mobile devices would also provide an excellent 'out-of-the-box' 2D and 3D user experience.
Will NVidia follow suit with NDA-free documentation disclosure? Lets hope so... it would definitely be enough convincing to get me to buy a Tegra2-based device.
 as in: whoops! this graphics subsystem only processes data at 1/2 the necessary rate! .... ahem... maybe you know who I'm talking about