I guess there are many theories to this question. In the comics, he can lift it. This is a fact! Also, you can lift it or can't. The idea you can sort of move it doesn't apply. Now, these are movies. So they don't necessarily have to follow this rule. I don't think we will know for sure until its explained in some fashion. But the fact he moved it a little is very suspicious of the fact that he really can lift it, in that he faked it. Some have said he was worthy, but he doesn't feel himself to be worthy so it didn't work. That one doesn't work! How YOU feel doesn't play into it. In Thor, when his powers are taken away from him, and he finally finds the hammer, he can't lift it, even though he does believe he is worthy. I totally believe he faked it -- there are too many references in the comics that you can. But, if you don't want to go by the comics lore, he was chosen because of his goodness in his Pure Heart, which was amplified after he had taken the serum. And it's very possible that Kevin Feige and the rest of the people involved in the storytelling don't even know either. That this is all just to keep this talking guessing which is working pretty well looks like.