That's extremely uncharitable. The major difference that you gloss over is that one has tools to stop fork bombs, but there are no tools to stop this kind of attack.

This attack can easily be used to disrupt systems. I can imagine every naive implementation of file upload out there being vulnerable to this. When the system goes to delete old uploaded files, it halts.

I'm not sure how "making deletes take a long time" is not a DoS attack.