I don't think it's that cut and dry. If a company paid a license for a development environment of some sort and had a development group that built customized behavior for the company in that environment, that company would consider that package an enterprise package. Perl, emacs, and the tools another group might build for themselves are no different, they are just free.
However, this example doesn't agree with brian's definition that if it breaks people will notice. If the tools the developers build with the package break, everyone will notice. If the tools break and the developers can't do their work, people will *eventually* notice.