So I’m not with MBI or anything, but let me see if I’m understanding this correctly: you’re upset because the company that makes your 3-D printer is selling a part replacement, you think is based on something you designed (probably based on a previous reprap design), and apparently decided to share with the community at large? If you cared about “owning” your contribution, why did you license it under Creative Commons in the first place? Or are you just upset at the implication of MBI selling this as part of a larger closed-source product?
I admit, it’s easy to just react reflexively at what MBI is doing as “Closed-Source = BAD!” But on balance, have they not been instrumental in helping advance the use of this technology in the first place? Isn’t their contribution to the whole worth cutting them just a little bit of slack? As a would-be entrepreneur myself, I have to say it couldn’t have been an easy decision to close source on the product. But seeing as how they’re betting their entire company’s success on being able to claw out a relevant piece of market share in a rapidly-growing industry, I understand their decision as one born out of sober necessity, rather than wishful thinking.