This reminds me of the sad fact that most distributions are just repackaging the same old GNU tools, or if embedded then busybox. Where's the innovation/experimentation of base userland? Android (other mobile linuxes probably too) is a nice exception, even though I'm not particularly fond of it as a system, I approve that at least it's trying to be different.
I wish there was a way to end this meme, so people didn't keep saying the same dumb thing every time: Changes to Plan 9 are continually integrated, with a new ISO being generated every day. Inferno lives as a Mercurial repository these days, and it too gets updated frequently. In Plan 9, for instance, they recently added a better bootloader and support for timed semaphore acquires (and after that patch, you can now build Go for Plan 9). We even get ports to new systems from time to time, like the beagleboard or the gumstix.
At the speed Linux changes, a 5-year-old Inferno would not even build. The lates available tarball is from 2010, but the reason a tarball is even provided is because it speeds up a pull from Mercurial. If you are interested in the current goings on, I've summarized some of them: http://debu.gs/entries/plan-9-and-inferno
Erm, GNU is doing the "innovation" here, i.e. adding spurious new flags and options. Which got quite annoying back in the days when I had to work with other commercial Unices and still hits me from time to time on BSDs (including OS X).
Many are actively developed, but simply do not share GNUs enthusiasm for adding new features. BSD userlands get plenty of love, but they are something I have little interest in using myself. Busybox also gets lots of development, but has much different objective than GNU. Both BSD userlands and Busybox are great.. in their niche; just like GNU is great in its.