Earning money

That model as such might be OK in theory, but in practice there often seem to be several problems:

- The "GPL" version as it's often called (it's usually GPL) is marketed as some sort of demo. This on its own will create resentment, and will stop many people from even considering looking at your software. Selling additional propriteray components is fine, (subtly) trying to imply that the GPL version is somehow inferior is insulting to the people who worked to make the GPL ecosystem great.

- What happens to outside contributions? Will you refuse a patch because it reimplements a proprietary feature? If so, prepare for some bad feelings.

- If these companies accept outside contributions at all, they usually require some sort of copyright assignment or unlimited rights to use the contributions in the proprietary version. The outside contributor often does *not* receive the right to also sell a proprietary version. This is fundamentally asymmetrical, and enough reason for many people (including myself) to not work on this software. (aside: I don't necessarily *want* to release my own proprietary version, I just want equal rights for equal effort. If you don't expect (at least) equal effort from the community in the long term, why do you even want this community?). Using a BSD style license would solve this of course, but one gets the feeling that this was a deliberate choice.