And it's not so different from the *nix shell mechanism of somekey=somevalue command.

On all Unix shells I know, the caller has influence on whether somekey would end up in his/her environment, not (like in Windows Batch) the callee. For instance, if I call from bash a script like this:

source gurgle.bash
[download]

no child is born and the environment changes will be reflected in my environment. If I call it like this:

gurgle.bash
[download]

or

bash gurgle.bash
[download]

I do get a child and my environment stays unpolluted.