I could still be using the original OS X. That wouldn't be free. But the (recent) upgrades have been.
You cannot run Linux on thin air. You have to buy/build a computer. Not free. It might be cheaper than a Mac, but that's the price you pay for a free OS.
And the thread started as Windows-is-now-free. If you haven't got a PC, you will still need to buy one to run Win10. But if you already have a PC you can upgrade to Win10 for free. Bit that's already the case for OS X.
Well that's disappointing. Making Win10 free for everyone (including pirates) was one of the smartest things MS have done for a long time. This pretty much negates that entirely.