The marketing strategy of Apple. There are different version of the latest Ipod touch. The cheapest is just above $200, the most expensive is $375. The difference? As far as I can tell, is the storage capacity. The cheap one's capacity is 8GB. The most expensive is 32GB, but there is an intermediate player at 16GB for $280. The only difference between them is the capacities.

So, for almost $200 more, one can get 32GB of storage. This is why they didn't put an SD card slot in the thing, they would only be able to sell one model, and leave storage up to the consumer, which can be had much cheaper with common media such as the SD card.