You make money on open source products by SELLING THEM, just like closed source.
And Just like Closed Source Software the real money is in Support Contracts not software licenses.
Companies make Money on OpenSource software all the time.
Apple is at the top tier for consumer open source sales.
Then IBM and Redhat make a boat load of $$$$ in the Business world on OpenSource Software.
You should also note, that even Oracle lets you download and use their database for FREE, you just pay out the $$$$ for support.
“Give away the razors, sell the blades.”
Ok.. you just go ahead and develop some application that you use to make money in your business with what you download from Oracle, and we'll just see how "free" it is.. Read their terms closely. Most of the stuff they have available for download are for your personal use only, and most have been disabled in some way as to make them useless when applied to an enterprise class application in a production environment. For instance, Oracle10g Express that comes with APEX.. Install that on your machine, and sure, you can develop with it, however no one else outside of your local machine can access anything that you develop with it. Great to learn with however. ;)