The 'not a career path' statement is probably not really true.
Most of us (DBAs, programers, administrators, etc) DO NOT write the system code in MS SQL or other applications. That is a relatively small group of people who do that. What WE do is make a living maintaining, customizing, updating, toubleshooting products that others have written.
Whether that product is 'open source' or 'closed source', free or paid is immaterial to our career path. That's not what we are paid for. So our general career path is the same whether we manage Mysql, SQL server, or Oracle.
I am a full believer in (especially) open format, and really open source even if the developer wishes to make money selling license to his work (I have no problem with that at all). Companies come and go. Developers make changes that break things, sometimes we need to move our data to other uses.... and open format (at least) is critical for that. Imagine if auto companies (some have tried, unsuccessfully) succeeded in blocking all information about the workings of their products and how to repair them. Imagine if the sale of auto repair manuals were prohibited as 'intellectual property'.
If someone wanted to steal software without license, it's easy to do. They certainly don't need source code for that. Similarly there is not compelling reason to close code to protect licensing stream. You can still have full legal ownership of your ideas as you chose.
-- FORTRAN manual for Xerox Computers --