Second, it is unlikely in the extreme that this music will actually show up in the final film. Hans Zimmer is scoring Man of Steel, and he and his team tend to bring a strong personality to projects. Finalized films do occasionally work in borrowed compositions, but this is usually because the director used it in the temp and fell in love with it. Die Hard did this. The Star Wars prequels. Three Kings used an odd bit of Thomas Newman's Unstrung Heroes. There are some more recent examples I'm forgetting. But the director of Man of Steel recently announced that they will not be using the John Williams theme from the 70s in his film, so they're obviously trying to give it a new stamp.
Third, it's actually common practice to use preexisting music in teaser trailers. Generally speaking, the original music for a new film isn't ready until shortly before the film's release. There's no new Superman music in the Superman trailer because that music doesn't exist yet. It is very rare to have original, film-specific music in a trailer. Obviously, The Hobbit uses original music. So did The Return of the King a few years back. Tintin's trailer used some of the original score last year, but that was because Williams scored the rough animation and held recording sessions at least year in advance of the film's release. (Additional sessions were held once the animation was polished.) But let us remember that even The Two Towers' trailer used music from Requiem for a Dream, not music by Howard Shore, so The Lord of the Rings has been on both sides of this equation. (And since people still ask, no, Shore had nothing to do with the Requiem music.)
So why is this causing such a stir? Generally when a trailer repurposes a piece of film music, they chose something with a low profile -- something accessible, but not strongly associated with a particular narrative. The end of James Horner's Aliens showed up in action trailers for years. To this day, Randy Edleman's themes from Dragon: The Bruce Lee Story and Dragonheart are probably better known for their many trailer appearances than for their places in the original films. Gandalf's fall, however, is an iconic moment in a classic score from a famous film. Does it work here? Sure -- but you could put Shore's beautiful music behind a video of me eating breakfast and it would still be inspirational. It's just that powerful. Is it distracting in Man of Steel? Yes, probably. At least for those of use who have lived so closely with the music. But I bet it will sell a lot of tickets at the same time.
Finally, as a result of my recent marriage, I am now related to the actor playing the bad guy in the new Superman movie -- so I'm keeping a safe distance from the rest of this brouhaha. ;)