This has nothing to do with windows. Nothing prevents software installed in Linux (or Os X) from installing crap Firefox (or safari, or whatever) extensions.
On a technical level you couldn't be more correct.
However, for various reasons – a mix of cultural and economic I suspect – ridiculous hidden installations and other software showing a coldly calculated contempt for the user are a fact of life while using Windows, and are very rare indeed on other platforms.
Nothing prevents it - true, but the normal method of installing packages is not like this. i.e. where every single file on the entire system is cataloged, and the exact program that installed it is known. Windows has nothing like this.
It has a unified place where programs can list themself, but the actual un-installation is up to the program. And it has no unified method of checking if programs are up to date.
