Except that it has, at least once that I know of, one a friend who build a 16 video card setup in a re-purposed NetApp filer box, cost them $4,500 to put together all told and they sold enough bitcoin on the first bubble to return a bit more than double that ($10K). That setup is too slow these days (and it ran for about 6 months, so figure the cost of 6 months of electricity at (basically 36kWH/day, which at 25c/kW added another $1638 to his cost, but his heating bills were lower :-)
What happens though is that the goal posts move, and of course if you get yours late and the difficulty has increased after you get one and you're under performing, well you lose. A number of people on the various forums claim to have made money on their miner setups as well but the forums are not really verifiable sources.
As far as I can tell it works when the market price for bitcoin greatly exceeds their cost to produce, and that seems to happen frequently.