I'm not specialists but I think that wole "X" series in Mac OS is Unix or Unix-like, the previous Mac OS (9 and below) was way another story (beautiful story...)
In Linux the source for any part of it is easy to get
Nope, if author doesn't want to reveal source code he/she doesn't have to, once again Linux license doesn't force ANYONE to make Open-Source programs, it just forces to make Linux be free and open-source, just that
Sure, look through the source and here's some tools to run.
Again, no willing to give source, no deal
In OSX the source and documentation for core parts is mostly inaccessible...
Once again, unless author wants to reveal the code
Wish this wasn't so, but people use WINE and such to deal how they can.
Yes but it doesn't work for GG/HS/othersuch[censored] things, as mentioned they are rootkits and Wine doesn't want to make them run, neither Linux itself wants, safe or not it's rootkit...the other thing is that GG is SO EASY to crack (well kick-out with game still run) but not everybody knows how to do it
End User must think not how to run the game but how to trick the game, that makes wrong politics of some sort, because instead user to be happy that he can play his favourite game on Linux, he must get the happiness by forcing his way to it...I don't mind such challenges but not everybody wants that kind of work to do

I still recall the guy that showed on Youtube how he has run Pangya (aka Albatross18 in the past) on Linux but didn't want to reveal the method because he believed to whole end of the world that if he will do it the company won't help Linux users...wha~?!
Anyway in my opinion we are still at the "hate" of companies to Linux...
IMO it's not problem to make program to be so-closed-source like on Mac OS X and to make it run on Linux
One more thing, if I would want to be "paranoic" about getting into source code by backward assembly, I can do it regardless of operating system I have (Virtual Machine FTW)
For example I install OSX on Virtual Machine, get the game, install it, play a bit, get it out to Linux host and use tools to disassembly it and what's more, if I will get source code there is HIGH chance I will be able to recompile it for my Linux platform!!! (just have to correct names of libraries names in the files and as worst case, get the ones that probably should not be in the network but they are anyway teehee xD)