Umm...you obviously miss the point of the iPhone. The iPhone is a phone on which you can install thousands of third-party apps, some of which are quite neat. Most of these did not take several months and a few thousand quid creating.

On the other hand a Nintendo DSi is a portable games console - i.e. a miniature version of a Wii/PS3/Xbox. Nintendo DSi games generally do not help you find a taxi, allow you to use Facebook on-the-go, etc. What's more, the developers of these games take several months, and cost a few thousand quid to create.

DSi != iPhone. Some people own both, and use whatever they feel is best for the task at hand.