Some people want real hardware that will actually mine Bitcoins at the advertised rate!
However, the devices are useless, because they will never generate any ROI.
Example: the USB block erupter:
Price: 70CAD (~67USD, ~0.5BTC at current rate)
Speed: 0.34GH/s
Power: 5W
So, if I get it this instant and start mining, it will generate about 0.08BTC/month. If the difficulty froze at the current 66M, it would take the miner a bit more then 6 months to generate the 0.5BTC I paid for it. However, difficulty is increasing really quickly, so in reality it will take much much longer to generate the 0.5BTC and it probably never will because the point where the 5W to run it costs more than it generates.
OK, the USB block erupter is a toy essentially, so how about the blade?
Price: 1900CAD (~1800USD, ~15BTC @$120/BTC)
Speed: 13GH/s
Power: 120W
If I plug it in now, it will generate 3.02BTC/month. If the difficulty stayed constant at 66M and I had free electricity, it would take a bit less than 5 months to generate the 15BTC I paid for it. In reality it will take much longer and probably will never reach the 15BTC before it starts producing less than what I pay for the energy to run it.
So, both devices will result in a loss, if you hope that BTC price will increase then spend the CAD to buy BTC directly or just keep you BTC if you were planning to buy the devices using BTC.
This is the reason why people pre-order stuff. If the unit arrives on time, then you will hopefully get ROI. While there is no risk involved in buying ASICMiner devices, there also is no profit (potential or otherwise), just loss.