Only 700 Linux preorders...
At first I though that maybe it was because the readership of Phoronix amounted to only that much, then I read the comments in this thread.
It's completely out to lunch to see so many self proclaimed Linux gamers (they sound more like Windows gamers, but anyway) offer so many rationalizations on why they can't find 20 bucks to support a company that has done more for Linux gaming than any I can think of.
Unigine has released all their benchmarks for Linux, when others just keep to DirectX and Windows. That doesn't come cheap. They've also got a solid track record for updates and supporting the Linux ecosystem - which is impressive considering how their engine can stress a system, and how Linux hasn't been stressed anywhere as much before. That's a far better track record than any indie I can think of - they release a world respected professional engine, and they do it in a way no other indie would even be able to dream of.
They've also offered their engine to promising indie developpers, on the condition they release a Linux version of their game.
Basically, even if the game beta wasn't offered with the preorder, that would still be enough to warrant supporting them - Oil Rush aside, they've already done far more to support Linux gaming than your 20$ could ever buy.
However, it's not all. The game runs beautifully at this time of development, and while they need to add content, it's not the hard part now - considering they have something solid at this time, and their track record of technical expertise, trusting them to add more maps is a no brainer.
At 20$, the game is also really well priced for a tower defense game. Tower defense is a really popular genre those days, so they're targeting some of the largest user base they could get with a game this price. Other tower defense games are similarly priced, yet their graphics don't hold a candle to Oil Rush, and Oil Rush gameplay is also deeper. It's an incredible deal.
It's also not only a day one Linux support, but prerelease and beta support as well. Most indie only target Windows, then port to Linux, so in the best case you don't have much access to the beta, in the worst you're waiting a few months after release for the Linux port.
We don't have much games running on Linux because the Linux market is the worst you could target, and I'm afraid Unigine is realising that, along with any indie or big brand developer who would have the curiosity to read shame of a thread. Look at the Mac market, even when they didn't have much they kept buying games and supporting what they had, though the ports were a disgrace and the games niche games they weren't interested in. The X3: Reunion Mac port is a joke (not even a port, more like the Windows game running through a subpar wrapper) and was priced more than the X3 native Linux port from LGP, yet it was received far better than all the slack the Linux port got from being more expensive than bargain-bin Windows games.
When you're buying a renowned game that already brought more than a million dollars to its developers (Minecraft), you're not supporting Linux gaming, you're just getting what you want, like any other customer. When you're buying the HIB for more than what Windows gamers paid for, you aren't supporting Linux gaming - you're getting a bargain, since even if you're only going to try one of those games a few hours, you're already getting your 15$ worth.
Oil Rush is more like a bargain for all you got in return (the engines benchmarks on Linux, the gift of this engine for other Linux indie game teams, and the game itself, which is already hinting at something better than most of the other 20$ tower defence games). And it's like what, two movie tickets, or a half-decent meal at a restaurant?
Maybe you can't part with the money, because your conscience tells you so. So what? Does it mean you have to be a prick, and backstab a game you haven't even seriously tried? Unigine is doing right all the things you guys used before as excuse for not supporting previous Linux native games - day one Linux support (better actually), same price as on Windows, and similar price to other games in the competition (better price actually if you consider you get a deeper gameplay and far superior graphics). From a company that has already done more to support Linux than we Linux gamers could have ever dreamt of.