I also doubt any translation service would want to 'evolve', because they get their profit from human translation. Why evolve something free to such an extent that you lose your income?
I think if it was possible to make a perfect translation engine, then it would be worth far far far more than a team of human translators as the computer would be quite happy to do it without being paid. Unlike the human version.
I very much doubt that is the reason why we don't have a near perfect translation engine in existance.
Though I'm sure if someone did make one, they wouldn't exactly cover it with the gnu license and stick it on sourceforce.net. Just too much money to make from it.
