There are a few dozen companies that sell these exact same parts, linking to the open source project. Should all of these companies stop selling parts just because one company has bundled all of the parts together? Is that one company solely responsible for all of the open-source development of the machines that existed prior to the Ultimaker, where is technology evolved from?
When you make something open-source, you are knowingly giving anyone access to your technology, and at least in the U.S., that is considered public domain and open for free use. If a company wants to be compensated for all of 'their' hard work, then they should not make the information freely available to the public. The 'spirit' of open source is to provide a means where anyone and everyone can build it, not to limit it to certain individuals or one company.
What is your opinion about the Stratasys and other printers where patents clearly exist that the Ultimaker is violating (at least in the U.S.)?? An open source project would be difficult to go after since afterall, it is a non-profit venture. A for-profit venture would clearly put the owners of the patent infringing device at risk for legal action.
The only action that should take place with these "knock off" companies is changing the name to something that does not imply "Ultimaker". I have seen a few that do just that, saying that their machine is "reprag" compatible, with no mention of the Ultimaker name at all - even though the box is 100% identical (minus the robot and Ultimaker logo).