If a drives data areas are overwritten with zeros, which is what I believe you are referring to, then using software alone is not possible. Software reads only one level of data on the surface of a disk.
If it was something that warranted it, along the lines of millions of dollars worth of data, or national security, then there is a technique for reading the data off the hard drive which involves removing the platters and reading the actual subsurface magnetic signatures, but that, trust me is not done on your average case. Or one in ten thousand for that matter either.
Tat is true, but with technology advnacing as it is, I have heard from some friends in VA that the technique has gotten better. To the point htat they generally get what they are looking for. And it has become more automated. The direction of the molocules on the surface and sub-surface of the disk are actually being read more.
That has got to be some very cool stuff to actually get to watch. But you make a very good point CC.