I forgot to add this to my very long post!
The Arudino site says two different things about licenses for the Arduino.
All uses OK
The main page says, and has said for a long time, that the design is licensed for however you'd like to use it:
"Note: The reference designs for Arduino are distributed under a Creative Commons license Attribution-ShareAlike 2.5"
The hardware versions page also says the same thing.
Commercial use not OK
Another page, for the serial single-sided board, had this added to it in 2006:
"Note: The reference designs for Arduino are distributed under a Creative Commons license Attribution-NonCommercial-ShareAlike 2.5"
I point this out as an example of how several different messages about the open-source nature of the project are being given: in this case literally!
It's probably a good idea to fix these mixed messages, to clarify what the licenses are, how open they are, and the rationale behind any changes.
D
Edit: bearing in mind that we're just talking about the designs here, this is what the Creative Commons web site says about revoking one license and substituting another:
What if I change my mind?
Creative Commons licenses are non-revocable. This means that you cannot stop someone, who has obtained your work under a Creative Commons license, from using the work according to that license. You can stop distributing your work under a Creative Commons license at any time you wish; but this will not withdraw any copies of your work that already exist under a Creative Commons license from circulation, be they verbatim copies, copies included in collective works and/or adaptations of your work. So you need to think carefully when choosing a Creative Commons license to make sure that you are happy for people to be using your work consistent with the terms of the license, even if you later stop distributing your work.
This seems to say that the Arduino reference designs continue to be under the CC 2.5 license ( attribution-share alike), since you can't change to a more restrictive license mid-stream.
So, what's the deal? 
Has the license been changed to a "non-commercial one"? If it has, that change would seem irrelevant by the above conditions of the original license. Everything should be open, and indeed it seems to be open without restriction, at least on paper, just as the original license says.