Not only that: take a look at Emacs: essentially no one Emacs is equal to another. It's so flexible that any users bend it (easily) to their needs and desire. Sharing their configs is a mean for any users to evolve, acquire knowledge easily; you have a problem or need something? Ok go look for others chances that they already see and solved that problem are really high. With "black boxes" you can only customize what black box dev's have leaved to their users, real changes are hard, you have to checkout code, study it, modify it, rebuilt, ... in the end you're became as "standard" as possible without freedom and personal experimentation even if you have the open code.

That's easy for companies since they deal with "standard" "Ford model like" people, but that's a killer for evolution especially evolution driven by people/users, not upstream/companies.

If you can tailor software to fit your needs as you like you get a friendly personal environment and you have "a bit of power" on society, you still need upstream work but you are also a bit independent, and the same is for upstream to have help from the community they need to comply with an heterogeneous community with users, not consumers. We are in the end interdependent so forced to cooperate in a relative peace. On the over side we totally depend on upstream being effectively powerless. Oh yeah, you can choose different software, at least for now, but that need to exists, that's no more a community.

A simple example a proprietary software, Master pdf editor, gain a bit of success in GNU/Linux world and decide to insert watermark on modify pdfs by free version. If it's distributed by single distro, single distros can keep old version for long time. Leaving all needed time to their user to switch. If you relay direct on upstream you discover the new "feature" a day perhaps without warning because it's auto-updated for instance, and you may have no time, no choice. This also happen recently with the "tweaked" Android settings by Google and I think many many other cases.

Freedom it's not only "being free of doing something" it's also can do something easily, have a system that let you be as free as you like.