Well, a much smaller percentage of Windows users are on 8.0 than OS X users are on Snow Leopard or later. If Blue allowed upgrades from Windows 7 for free, that'd be a more equal comparison.

That would be incorrect. There are more Windows 8 users than ever version of OS X combined.

Sources: http://appleinsider.com/articles/13/09/02/windows-8-jumps-pa...

http://www.netmarketshare.com/operating-system-market-share....

That's not what he said. He was speaking in percentages relative to each install base.

Mavericks is free from Snow Leopard onwards (because Leopard didn't have the appstore).

In terms of period that's equivalent to giving 8.1 free to all W7 users (both SL and W7 were released mid-2009)