Dell engages in differential pricing, so you absolutely have to "buy smart" when dealing with them. On the other hand, Apple has consistent prices across the board.
Basically.. Dell accepts that some customers are unwilling to buy from them at their regular prices. They believe that, as long as they are still making money, it is in their interest to try and make those sales anyway. Hence Dell has occasional, but spectacularly good, one day only specials. On the other hand, Apple believes that maintaining the perceived brand value is more important than catering to customers with low willingness to pay.
You can see very clearly in this thread that they are both right. They both understand exactly what markets they are catering to, and do a very good job of marketing and pricing to attract customers that suit their own business models.
Kind of makes me sick, to be honest :)
Whether you prefer paying for "perceived brand value", or patiently waiting for discounts, which have the consequence of feeding the beast, is completely up to you, of course.