Of the thousands and thousands of illegally "shared" games/songs/applications/etc it is safe to say that a significant percentage of those people doing the sharing would have otherwise paid for these products.
It is actually more likely that the percentage who would pay is relatively miniscule because if the downloaders were actually willing and able to pay the asking price, they would be doing it. Anyone will take something if it is free. The notion that someone would have paid for dozens, hundreds, or even thousands of songs, movies, or games simply because they had downloaded them for free is ludicrous. If file sharing did not exist, would these downloaders have purchased ANY of the things they had downloaded? Sure, it is likely unless they were pretty impoverished. However, would it be a significant quantity? Most likely not since they could not afford it or would not otherwise spend the money on it.
The bottom line is that even if copyright infringement via file sharing disappeared tomorrow, there still wouldn't be enough sales revenue to keep all of these companies which claim that such infringement is killing their business afloat.