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Sure, OO was and is free. But I'm more than willing to pay money for software that I know is useful. A free version of a not-very-useful program is still a not-very-useful program.
Bringing its pricetag down to zero does not change its native behavior. It simply makes it that much easier to find out whether or not you're going to be happy with it. In an age when you can get a free 15-day trial of everything from MS Office to Photoshop, it's that much less significant.
As for the philosophical value of open source: The fact you can modify the source means nothing to people who barely have enough time in their day to read their email, let alone learn how to program.