I'd disagree with this. While OS X and Windows are not as transparent as linux, there are enough resources on both that a hacker that wants can go deep on them. In the Windows ecosystem, Mark Russinovich (creator of Sysinternals) and Charles Petzgold readily spring to mind as people who fit the definition of hacker.
The biggest difference is that if you run Windows, you have to be willing to crack open IDA and read some assembly to really get a view of how your system is doing something sometimes.
The main reason I keep a Windows box around is because so many Windows devs seem to think that security through obscurity works and that no one is willing to patch their binaries. Big mistake.
