That game has been free since the source was released I think and remember that the game has been out a long time.
I agree with the focus, but you also need to remember that DDI is a business, it needs to make money to survive. You can't make money on a free source code.
This is an odd statement, not because it's not true (which it is), but because in theory it IS true. You can sell a game's compiled binaries for an arbitrarily ammount, and you can release the source for others to compile. What you're effectively selling is the labor it took to compile the game. Believe it or not, there are some people on the internet who don't know how programs work, let alone what a compiler is. Those are the people who would buy the game so they don't have to learn about compiling programs and such. More experienced people who know how to use a compiler would have the advantage of being able to build their own version of the game.
Now, the issue is people selling their version of the compiled game. This would only work if the original game designers didn't bog the game down with copyright stuff. Then again, the one who wants to sell a modified version of the game then is in the same situation as the original designers. Odd, isn't it?
Growl is a good exampe of this. Yes, it's completely open source, but the binaries are not free. If you know how to use Xcode and the proper software version control program, you can obtain and compile the source and install it yourself for free. Or for $4 you can easily get it precompiled and installed from the App Store.
An OS X build would be nice and probably not too difficult if a Linux version were made.
Before people start throwing rotten tomatoes at me, I don't really support or even prefer Apple. Honestly, it's getting to the point where I hate all operating systems, especially Windows 8. OS X is just a school requirement and so my most powerful computer is a Mac.