It's what you see in fields of all sorts. There's your top 1%, top 10%, top 25% and then all the people that need to fill the seats but if actually had to compete in a limited market would be gone.

And after you modify your source version of the code, congratulations, upgrading to the next version is at best case going to require careful thought and planning, and at worst case a lot of time and effort on your part.

The danger of customizing your open source product is the same danger that companies face modifying products like SAP. Once you go so far down that path, upgrading is prohibitivly risky and costly.