From what's been released this is obviously one of the most challenging aviation disappearances ever; however, given the location of the world in which it happened you have two very interesting factors at play (which either the pilot(s)/hijackers considered or got exceedingly lucky).
1) It appears Malaysia doesn't have the infrastructure to figure out what happened entirely for just the time the plane was in its airspace. They could be leaving out details, but even if they are it seems like they don't have a clear picture (maybe that's exactly what they want us to think?).
2) You've got countries like China and the U.S. involved. Let's say it DID land somewhere in remote China. In that event, China is probably the only country that could announce they found it. Can you imagine if the U.S. located the plane in China? There may not be many, if any, ways we could tell anyone we knew. "Hey China, you can't see it but with our super-satellites that are constantly spying on you we've located it the plane!" This is similar to the pictures China released early last week with photos of potential debris. The resolution was terrible. I highly doubt that is the original resolution, but China doesn't want to announce just how good their capabilities are.
From what I've heard on the news it sounds like Malaysia is the only country that is allowing other countries participating in the search into its airspace. Which means all other countries are searching only in international waters, over their own land or perhaps via whatever satellites they have. Some it's entirely possible somebody does know where it is, but either they don't want to say because they are complicit or they can't say because it would have even greater implications.
