It is the wicked beauty of iPhone Apps. My best example of this is Koi Pond. It's my favorite app to show off for the iPhone because the 'function' is simple yet it's visually compelling. Among so many apps - including the popular ones - that are awkward or simply ugly aesthetically, Koi Pond stands out. A great feature for traveling, you can set a timer on this and have a white noise effect of the pond sounds (which you can adjust) to help relaxing, napping or sleeping (up to 12 hours). So far this is one of the most thoughtfully and elegantly designed apps that I have seen and used.
Watch the demo by the designer to see some of what I mean.