Not totally sure either, but my best guess is they're aesthetically pleasing and supposedly ergonomically great, which is I guess appreciated amongst the crowd that spends all day sitting in front of them.
yeah... my first thought was 'orange? really?' It just seems like they are going to look very dated in a few years. I mean, I kindof like the look of the aeron, but part of that, I'm sure, is that I came of age during the dot-com, when they were super cool. I'm still kinda disappointed in myself for not getting one at a dot-com closeout. That would have been... appropriate.
I have a few '70s steelcase chairs... they are not bad chairs, they are still in pretty good shape and work okay, but the avocado green is... avocado green.
I think the color choices selected and used for their website is more to highlight the chair design and not actually a color people would choose themselves.
We just outfitted a conference room in my office and they selected a color that I've dubbed "poopacado."
They seem to have a fair amount of research to back up their ergonomics (see this blog post regarding Aeron chair design: http://www.hermanmiller.com/research/solution-essays/the-ben...)