When Age Of Ultron first screened there were some complaints from comics purists who thought the changes to origins were somewhat unforgivable. Artistic licence covers a lot of that, but the really compelling issue was whether Steve Rogers should have actually been able to lift Thor's hammer all the way instead of moving it just enough to squeak the table. He certainly has been "worthy" to lift it in the comics (in Thor #390, among other occasions). Perhaps the Captain of the Marvel Cinematic Universe, who is still just a bit of a little boy at heart, is almost worthy but not yet seasoned enough to be ready for such an honor. But sushigrade's theory that Cap actually gave up on purpose is not only entertaining but it may even be true.