The pings coming from the Indian Ocean could be practically anything, the black box from the missing plane is surely a long stretch. People badly want this situation solved and over, but there's no reason to believe the pings coming from the ocean aren't some other waterproof electronic, toxic waste, or simply an error in determining.
It's perfectly reasonable to believe that the pings are from the plane's black boxes, as there's no reason to believe they're from anything else. If the pings aren't from the black boxes, there would have to be something else in the area to cause this. Without locating another cause, the most likely conclusion is that they've found the plane's black boxes.
I think that the search and rescue team is well trained in what exactly to look for when trying to locate a missing plane and if they have reason to believe that these pings are coming from the missing flight then I would be inclined to believe that they are on to something.
As terrible and cruel as it may sound, I think that we better start to believe that this plane will never be found and therefore, we will never know the truth about what really happened to those poor people. I think that the only thing we accomplish with this suspense is increasing the families' suffering.