The statistics of the "who wrote Linux x.y.z" series date back to at least 2.6.20. According to my experience talking with users and Free Software enthusiasts, those statistics really make a dent in the public perception of who is giving back upstream.
Obviously, one should not take a single upstream, even if it is as important as the Linux kernel, as a measure of how much a given Free Software entity is giving back upstream overall. But users still seem to be fascinated by them. As a result, I have often had to answer the question: why Debian doesn't show up on those statistics?.
My answer has always been something along the lines that Debian Developers who maintain Linux kernel packages, the almighty Debian Kernel Team, do that mostly as part of their volunteer engagement in Debian. As a consequence, they do not earmark their contributions as if they worked for a company and they add up to the hobbyist count instead (although you can you can routinely spot individual Debian Kernel Team members among the most active contributors for specific Linux releases).
The above is the true and honest answer. But every time I've given it, I couldn't help feeling that the user who asked went home with a "yeah, well" afterthought.
If you don't want to take my word of it, fine. Here is what Greg K-H had to say about Debian contributions in a recent blog post about the stable Linux kernel:
I would personally like to thank the Debian kernel developers, specifically Ben Hutchings, Maximilian Attems, Dann Frazier, Bastian Blank, and Moritz Muehlenhoff. They went above and beyond what any "normal" developer would have done, ferreting patches out of the kernel.org releases and the different vendor kernels and bug tracking systems, backporting them to the 2.6.32 kernel, testing, and then forwarding them on to me. Their dedication to their user community is amazing for such a "volunteer" group of developers.
I firmly believe that without their help, the 2.6.32 kernel would not have been the success that it was. The users of Red Hat and SuSE products owe them a great debt.
Buy them a beer the next time you see them, they more than deserve it.
I'll take good care of following his wise advice. Please do the same.
(Thanks to Sylvestre for pointing me to Greg's blog post.)