I believe if you're going the Homebrew route you're accepting the cask's versions of things as a means to synchronize installations. This could be handle for teams that need to be using the same versions of specific libraries or apps, system administrators who want to manage upgrades paths, etc.
It could also be as simple as "that's the way it works because that's how homebrew works". It's all symlinks, and I personally am a fan because if I want to cleanup what's been done with Homebrew it's very easy.
I do completely understand your point, and agree to a certain extent, but I'm sure there are situations where you wouldn't want things simply copied and left to run/update on their own.
I don't think this synchronizes installations since the forumla[0] are overwritten with each update. If someone updates one of them the specific version you downloaded elsewhere will not be downloaded again. I definitely understand why homebrew works this way, but the logic for symlinking the applications is all in this extension[1] so this could easily be changed. I agree that symlinks is better for tools typical to homebrew but for this it's not like it symlinks your preference files so you're not actually cleaning up any junk if you uninstall the application through cask, it's the equivalent of just dragged it to the trash. Also the applications will still attempt to update so it's not managing versions that way either.
It could also be as simple as "that's the way it works because that's how homebrew works". It's all symlinks, and I personally am a fan because if I want to cleanup what's been done with Homebrew it's very easy.
I do completely understand your point, and agree to a certain extent, but I'm sure there are situations where you wouldn't want things simply copied and left to run/update on their own.