I think 5D mark III targets mainly those who currently have a 5D (or mark II) and a 7D - both specs-wise and price-wise, and perhaps should not be seen as a typical 5D line camera. So the poll out of curiosity...
Good question. I would say it's for current 5DII and 1DsIII owners. The price is about the same as when the original 5D came out and that one and the II have proven to be hugely successful. So there is a market for very good full frame cameras.
I would think it's also (sort of) a replacement for 7D shooters since they may be faced with their line in it's current form going away. Why? Because it didn't sell well. Expect to see some plasticky version of the 7D line merged with the 60D. Just my guess and I'm not saying that it makes sense for the folks who like their 7D but that's what I think the numbers may indicate that I saw somewhere.