[magic_quotes]

> why is AMD able to ship more stable drivers?

Well, they don't — AMD drivers for new hardware famously take a few kernel releases to stabilize. (G)GP specifically noted their stability problem started only 5 months ago, which means at least that issue is not really systemic. The real differentiator here is handling of existing complaints: Linux has mailing lists, Mesa has a normal open for everyone bug tracker, while Nvidia has a user support forum, which they mostly ignore.