There are a lot of grammatical rules that can be acquired unbeknown to us by reading a lot and by listening a lot. But that is not the case when GT is searching through a huge database relying on some kind of statistical analysis. It cannot learn what we humans can learn, I suppose.
I am tempted to think that GT is rather like LingQ. Previous machine translation methods focus on teaching the computer the grammar rules. It is a complex and difficult task. GT doesn’t use grammatical rules. Lots of content is fed to the computer to let it work out its own rules. It’s kind of like how we LingQ users forgo formal grammar learning and just trust that our brain will be able to sort out how the target languge works based on a massive amount input. It’s not an exact analogy, but the similarities are interesting neverthelss.
No, not exactly like humans, of course, but a great deal of research has been done in the area of artificial intelligence.
Now, don’t get me wrong, I don’t believe for a second that machine translation will ever come anywhere close in accuracy or naturalness of human translators. But it certainly can be improved.