Actually what it means is that shelf space is expensive. A $50 MP3 player has around a 30% profit margin. You can stock 500 MP3 players in the space that one computer system takes up. A computer system has razor thin margins. It's not profitable to stock them on the shelf at your local Wally's.
Note that they still sell them on-line. Well, when they aren't sold out.
That’s essentially what I said. If they can’t keep them on the shelf, the price is lower than it could be without affecting unit sales, so they should raise the price a little and see if demand slows down to meet supply.
When they raise the price, they will get a better margin on the item in question. If the process goes so far that margin/ft shelf is better for the item than the one next to it, adjust the shelf allocation a little.
Your comment takes into account the reality of computer sales, I was just pointing out some general rules that apply to anything which they were apparently failing to follow.