The interpretation I like best is that people simply aren't looking. Superman seems to be there, rescuing people, day and night. They just assume that Superman is Superman, all the time.
I think that interpretation is out the window due to Zod's ultimatum...
"For reasons unknown, he has chosen to keep his existence a secret from you. He will have made efforts to blend in. He will look like you. But he is not one of you."
That said, I never liked that interpretation because the world is a big place and Superman is significant amongst it, so it's a little dubious to me that all of humanity would be so monolithic as to make that same assumption about Superman.
Lois technically figured it out
And would imagine Pete has to know as well!
I think it was Goyer that said there are quite a few people in Smallville that know Clark is Superman. I also think it's hinted that Perry knows as well.
Yeah, people knowing doesn't break tradition. Pre-New52 (and I guess now in the New52, Luthor knows) just short of a hundred individual named characters knew Bruce Wayne was Batman. Superman's identity was also widely known. The two issues are: a) What do you do with that information? b) How do you keep others from getting that information?
With regards to the first, The Dark Knight, covered this well enough for a movie and the logic extends to the DC Cinematic Universe going forwards. The accountant / would-be blackmailer actually shows all three things that can happen if you have the information:
- Loyalty - After Bruce Wayne saves the accountant's life, he earns the man's loyalty and silence. In the case of those from Smallville, they know Martha Kent, they know Clark Kent and what he's done for them (now that they know it was actually his intervention and not divine accident); the same for those he met along the way as a guardian angel.
- Self-Interest - TDKR shows a number of consequences that can arise if you disclose that you have this information. You could incur the wrath of the vigilante. You could become a commodity to his enemies (why pay you for your information if they can extract it from you against your will). You could be targeted by loyalists (uh, to the extent that Joker wanted to preserve Batman's identity). The same holds true for Superman. In this world, there's no known contingency against him... do you want reprisal from him? He saved the planet... do you want reprisal from the grateful? The US Government disappeared a prominent journalist on the mere accusation / suspicion of information, who no doubt will report loudly about her civil rights violation afterwards... so when the Men In Black come asking questions do you volunteer?
- Half-Baked - Of course, not everyone is going to think it completely through like in the two cases above. However, the natural consequences of your actions may tend to mitigate the issue. If you go to a loyalist, they may stop the spread. If you go to an enemy, trying to bargain for the information, they may threaten your life causing you to disclaim the information to avoid future issue. Honestly, you can't cover every possibility, but you can cover it enough for a particular story and all fiction with secret identities have been doing it for ages...
Preventing the acquisition of the information is another analysis for when I'm not supposed to be working.