It's useful to think of the copies of BSD-licensed software as OO-style object instances. Once the router company clones the source, it becomes this new code-b

It's useful to think of the copies of BSD-licensed software as OO-style object instances. Once the router company clones the source, it becomes this new code-base, that they can add to, without revealing those new changes. You are still allowed to make any changes you want to the original code-base, but: 1. That is not the code-base you want. You want the one running on your router. 2. You don't have all the build environment, and toolchain magic needed to produce a new binary blob for your router. Also, blah blah DMCA.