Tough little animals! What I wonder is this... how in the world are there logical explanations for the evolution of this kind of creature? Or is it time to consider "over-engineering" from an evolutionary point of view (of some reason freaking out with the positive mutations.. strengten already strong traits)? Under what conditions did the water bears evolve to bring forward this type of survival skills?
As I take it, your point is that on the one hand these creatures are meant to be products of evolution, yet on the other hand they have abilities that can never have been selected for by natural selection.
(While I'm answering this, you might think about how we evolved the ability to click our fingers.)
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Now, first of all, we can see how water-bears could evolve to survive dessication by going into anhydrobiosis. For clearly, in a creature that lives in shallow water with a possibility of it drying up (as water-bears do) an ability to shut down its metabolism and wait, in drier conditions, for a longer period of time will carry a selective advantage. You will note from wikipedia that the mechanism for doing so is not complicated. So we can see how they can evolve this trait.
Now, all the other traits follow from this.
If they can shut down their metabolisms, they can certainly survive ten years like that. Surviving ten years
functioning is more of a strain.
Now consider their cold-resistance. Why would cold kill
you? Well, the function of enzymes is temperature-dependent --- but the water-bear, in anhydrobiosis, has shut down its metabolism. It doesn't need functioning enzymes, it needs them all to stop what they're doing.
Another problem with freezing people and bringing them back to life is that in freezing, the formation of ice crystals damages the cell walls (hence the mushy texture of frozen vegetables). But the water-bear is dehydrated --- as the wiki article says, down to 1% of the usual water content. No problem there.
Heat disrupts organic chemicals much more when they're in solution than when dry, though unfortunately I am not enough of a chemist to explain why.
The wiki article you quote says of radiation, again, that "their lowered hydration state provides less reactants for the ionizing radiation". In short, it's again 'cos the absence of water changes the chemistry.
And the vacuum of space? Well, we've established that they should stand up to the cold, and they don't need oxygen 'cos they've shut down their metabolisms.
In short, they survive these conditions because
nothing happens to them under these conditions: it's not that they
fight off heat, cold, radiation, etc. And the reason that nothing happens to them is because they've shut down, and partly because of the way in which they've shut down (anhydrobiosis).
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And the reason we can click our fingers is that we evolved a certain amount of manual dexterity for other reasons, and that the laws of physics say that if you strike your middle finger hard enough against the ball of your thumb, it'll make a noise. So in a sense, we evolved the capacity to click our fingers --- but
not in the sense that this is a trait that was ever favored by natural selection.
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