Now, I understand the concept of a loss leader. They (in this case, a combination of the store and the manufacturer) don't really want to sell me a hard drive for $40 or a DVD burner for $20. They're taking a small loss and in exchange, I go into their store or browse their website. Customers in the store are the only ones who buy things. But part of offering loss leaders is taking that loss.
What they're really doing is a bait and switch. They baited me into the store, then didn't have the product they advertised. Instead, other sizes of hard drives or SATA drives were available. If they're not willing to stock enough of the item to meet the demand at that price (even the web site is out of stock on the hard drive), they shouldn't offer such a rediculously low price.
As part of my self-therapy, I note that the hard drive only has a 1 year warranty (3 years is standard). The sour grapes argument really does make me feel better. A little.