The resolution and quality of satellite images are different for different satellites, I am sure. That's why it was asked for owners of other satellites to reposition them so they could pick up info from this specific area.
On google street view I can see my car in the driveway. There would not likely be satellites with that type of resolution being aimed over the entire Indian Ocean.
I actually think it is pretty amazing they've identified something as small as approx. 70 some feet long. I also think it's important to take into account that the former director of the National Transportation Safety Bureau has stated that he thinks this object is too big to be a part of the plane. He would be one of the most knowledgeable experts on earth about these kind of things, so I'd give credence to what he has to say.
Obviously, they could not ignore these findings so they are doing what must be done in order to further identify them. And yes, they had to make it public right away due to resources being immediately needed. Asking merchant ships to participate is unusual and extraordinary. That would not be kept under wraps for long.
This Australian government site says that a general maritime broadcast went out on Monday evening. It also says that six ships participated in searching.
http://www.amsa.gov.au/media/documents/20032014MediaReleaseUpdate7MH370FINAL.pdf