Seriously, how many Linux users compile their own software? They don't. They just pull it from the repository where the distro provider looks after the dependencies.
Users might not, but they may well use third-party software not sourced from the distro repository.
Also the distro repository doesn't always take care of the dependencies that well, you can't rely on it. That's the whole point I'm making, the individual libraries are all individual little open source projects that happen to have been selected to be part of the distro repository. No promise is made that the distro cares about dependency compatibility ... they'll just continue rolling out updates to the individual packages. They simply do not have the manpower or the will to cross-check every single dependency for compatibility with all the other packages they distribute. The distros may also remove packages at a whim. That is why the closed source model of documented exposed APIs is better.
I'm not anti open-source, its just a case of the right tool for the right job. For the average home user, the hassle of open source is really not worth it when the Microsoft or Apple communities are larger and better supported.