Minecraft is not very taxing on the computer. It's rather lightweight, especially if you tone down your draw range and such. BUT, for what it is, it runs very heavy. If it were done in a more traditional language, you could get the same Minecraft with much much lower weight. The thing is... Minecraft is just simple. Even in inefficient Java there's just not a whole lot going on that taxes your system. It's a case where complexity trumps efficiency. You could design a calculator that runs terrible terribly slowly, but even if it took .5 seconds to run a problem people would still look at that and say "Oh it's quick!" Maybe you could design it better and it'd only take .1 seconds to do the same thing, but people wouldn't really notice the difference. Similarly, Minecraft runs at respectable FPS using a solid chunk of memory and CPU. It could achieve the same FPS using lower memory and CPU, but people don't much care about that. They just see "60 FPS is good FPS" and it's fine.
Notch has mostly relied on computers being strong rather than making his code good. Which is not to say that his code is bad. It's just that his code is in Java. I doubt 0x10^c will be in Java, so we'll see what the system specs are. I'd still bet it runs very lightweight, perhaps lighter than Minecraft depending on how much you have going on in a scene.