The Bitforce 50GH/s miner costs $2,500 today, and according to the following calculation it would mine enough coins in about 5 days to pay for itself.
I am sure I am missing something here. Why would they even sell this hardware at all? Surely it makes more sense to keep the hardware and just set it loose on calculating coins and cash them in.
There's a factor called Difficulty, the more hashing power exists on the network the more difficulty exists, therefore it's harder to mine coins. Right now The difficulty factor would let you recover your money fast because almost no one has ASIC chips, when they ship in bulk the difficulty factor will rise to 30-120 million during the year. To know by how much the difficulty will rise it's impossible, so it's your call.
Not if you don't have one already.
The trouble is that you don't know when you'll receive your device and, as @user3418 says, the difficulty will be rising in the meantime.
Butterfly Labs (who manufactures the device you're talking about) has only just started delivering devices, and already has a large number of pre-orders. You probably wouldn't receive your device for at least several months, and there's a possibility the device will never earn enough to pay for itself.
ASICminer did decide to keep the hardware and mine. They're selling shares with intent to payout the dividends from whatever profit is made.
However, Avalon and BFL didn't choose the same path. As to why, some people believe it's far better to "sell the shovel" than "dig for gold". No one knows what the exchange rate or mining difficulty will be in 3 months (things that affect profits for miners, along with electricity), but none of that matters to the hardware companies, since their profit will already be in the bank.
And the increased difficulty is precisely why the machines won't pay for themselves in 5 days. The might if you had one right now, when difficulty is low. But the network hash rate is going to increase by a large factor once all the ASICs have shipped by this summer.
Eventually, your single 50GH/s machine will be unprofitable as new, more efficient technology debuts and the network difficulty continues to climb.
They would if yours was the only one delivered.
Claim is made based on current difficulty rate. When ASIC miners ship to many people, difficulty rate changes rapidly. Total sum of profits all miners remain same, no matter what miners buy.
if you really want to see what you are going to make with such a device, use this calculator http://www.coinish.com/calc/ and set the Delivery Time to whenever you think your Miner will arrive, lets say 4 months. You will see that with the current trend, breaking even will take much much longer
If you sell them on ebay they may pay themselves. I think a better way to get into mining is to try cloud mining with cexio at least you don't have to wait, you can sell and buy GH/s whenever you want (maybe making a profit out of it) and you don't have to spend time taking care for the machines.
