Linux provided the most money on average for their portion of the sales, with OS X users coming in second, and Windows coming in at just over half the amount of money that Linux users contributed.
Besides any point this might make for one side or another of this argument, I just have to interject that I find this kind of statistic really cool. Why can't people bring more statistics like these? Not even the results in particular, just the fact that it exists. It'd be just as cool to know if Mac was the highest, or Windows
Now, on to seriousness.
At the moment, I use Linux mostly as a server OS, but I'm leaning more and more towards making it my primary OS (the amount of work that would take me is holding me back). I'd strongly argue for a Linux version, not just because I want to use Linux in the future, but because I don't see it as fair that because of a personal (and sometimes necessary) preference of some users to use a different OS, means they won't be able to play FTB packs as easily. This just appears to be blatant discrimination to me. Other people will almost certainly see it differently to me, and I respect that, but there's no point trying to argue this point, at least not with me.
Curse almost certainly has enough money to put on a coder or two to write a Linux version, they seem to be doing pretty well. And as people have pointed out, using a multi-platform library (or whatever it's called), while it would introduce a higher CPU use, wouldn't be outrageous and I doubt many users would notice. I think I saw someone mention 4% higher or something somewhere earlier. If your computer can't handle a 4% increase, I'm not really sure how it handled FTB modpacks in the first place.
I know that the mods will be available for manual download (and I assume the configs too), and that's better than nothing, but in reality, FTB managed a three-platform launcher on no pay for coders, how can Curse not?
Think about this: how would everyone on Windows feel if Curse was a Unix based company and they were only going to be making clients for Linux and Mac? Everyone on Windows would have to do what Linux users are likely going to have to do, manually download and construct the modpacks themselves. Now, looking at the reality, this isn't what's happening, but imagine how you'd feel if you had to do that every time you wanted a different modpack, then realise that some people
are going to have to do that, and those people are going to feel exactly the same boredom and pain as you would.
My last reference to the reality of things is that Curse is a company, and they must make a profit. They will, I'm sure, try as hard as they can to please the community (especially considering the initial hugely negative response from said community), but the harsh truth is that companies, Curse or otherwise, cannot stay running if they do not make a profit. If they could manage to keep the company running at a loss to please the community, I like to imagine that they would. But, that's just impossible.
Then again, I also believe that hiring Linux-specialised coders or rewriting the client to use a multi-platform library wouldn't actually put them at a loss anyway. I have no evidence of that, all I can do is be proven either right, wrong or "no comment" by Kaelten.