News Nvidia showcases quad-core Tegra 3 silicon

Mobile Hardware is moving SO SO FAST

 

Space is actually not that simple, radiation and other factors (high energy protons, etc.) cause faults that you wouldn't normally get on earth: random bit-flips in memory and even while processing. The smaller the fabrication tech used in modern IC's is more susceptible to these kind of problems. So instead they're likely to use larger fabrication processes, though that's still not perfect. A common approach used, especially in deep-space probes, is to use an odd-multiple of discrete computers (e.g. 5) and take the majority answer from them.

There's also issues surrounding predictive caching, multilevel caching, paging; super-scalar architecture and the like, that can cause problems in hard-real-time systems so they'd probably want to rip everything apart anyway. And if not you write software for the worst possible case so the extra performance is largely pointless (though it might save power in the long run).

Hence using older hardware, built on larger, more reliable processes that tend to not to have the less predictable performance enhancing technologies: