Not sure if I agree with your assessment of the Arduino situation as it relates to 'open hardware'. I think the differences in developing hardware Vs software are fundamentally different. Not even sure I have read a good definition of what 'open source hardware' even means. Just publishing the schematics could be considered one form of 'open hardware' and many project authors have done that in the past well before open source software project became popular or common. Perhaps it's releasing all design files including PCB files used to 'copy' the PCB design? I'm also not so sure that hardware development lends itself to collaborative design as easily as software development.
So whatever a correct or even useful definition of open source hardware is, I don't think that the Arduino as a company ever attempted to engage in an initial collaborative effort to design their hardware. The Due project seems to be the first where they stated they were or did release initial beta versions of the hardware to selected people for feedback before the final design is to be released for that project. We, to the best of our knowledge have not heard from any parties privy to the Due design effort.
Lefty