This is why many software developers now retain some portion of the actual software on their own server and the source code is not completely open anymore.
I'm not going to say it's wrong to do it this way, but if you are going to release a script with all needed components to run on a server, there's going to be a certain number of people who will steal it. Music, e-books, and movies fall into a similar predicament.
And that is exactly why the next software company I created is not open source, and is purchased as a service.
And this leads me to my next point. When people must keep paying in order to keep using it, the software developer must keep making the script better. If it is just a one-off purchase, the software has a great likelihood of becoming obsolete later.