I'm not sure if I'd agree with a 'very large chunk', but certainly I don't think this is an isolated incident. It's just that people don't usually make a fuss.
I think the basic issue stems from the fact that LKML sees patches as 'proposals' unless they can be included as is without further work. And any would-be contributor would be (heh) able to see that for themselves by looking at the many years of documented interaction between maintainers and the general public.
These long running projects all have their own styles and conventions for interaction (LKML itself being one of those) and the onus is on newcomers to familiarize themselves with that. Authorship, especially in the context of a project of this magnitude and with so many different people maintaining different parts of it is always going to be somewhat nebulous, because after all, you're changing a tiny little bit in a huge machine and anything worthy of copyright is usually expected to stand alone as a 'work'. That's definitely not the case here. And so the sign-off becomes a critical bit, if you omit that then you've just created a problem for the maintainer. Personally, I would never expect to be named author of a patch sent to the kernel mailing list, but if I wrote a sizeable subsystem then I would definitely expect that kind of recognition.
For patches like this your pay-off is the fact that they are taken into consideration at all.
