Briefly, I believe the "debris" or object spotted by satellite in the Indian Ocean was located via a commercial satellite - probably around 700kms above - many of these satellites are only able to create sketch grainy images due to the angles and height. Apparently in comparison, military satellites are able to be lowered to 100km above and beam in using the correct angles - enough to read the headlines of a newspaper that a person is reading - they would be able to identify it as aircraft debris if so.
The problem here is time and fuel - as many of these satellites have limited fuel capacity - with of course, the public use of highly classified technology that most nations would not want to share.
