Crossing genres in live-action is harder than in comics indeed, but not impossible or even close to it. Marvel essentially did the same thing and managed to pull it off. For the most part, Iron Man focuses solely on the tech side of the Marvel universe with zero focus on the rest. Favreau even stated that Iron Man's realism was inspired by Batman Begins' realism, and even incorporated a lot of real life issues such as terrorism to give it more of a real feel. Sure that the MCU toned down Thor's mythos to an extent (which they seem to be fixing with The Avengers and Thor: TDW) but ultimately, everything fit in well for the most part.
Also, MoS was not trying to expand on the DCU outside of small cameos to WE and things of that nature. What it mainly does is expanding the Superman mythos. The Batman films will expand the Batman mythos, the WW films will expand the WW mythos, the GL films will expand the GL mythos, etc. Obviously that the concept of magic won't be alluded to in MoS due to that. I prefer things to be this way. I was never fond of the way Marvel turned most of their solo films into Avengers promos as opposed to letting them stand on their own.