If you look at the graph, you see that iPhone users generally use more bandwidth. But the usage patter is interesting. When you get to the highest user category, usage by iPhone and "other" smartphone users is equally. Where iPhone users consume more bandwidth is in the range of 50 MB to 500-1000 MB.
In fact, iPhone users follow the most expected use curve, with a bulge in the middle and a slope along the ends. The "all other" category has a huge bulge in the 0-50 category and then a sharp drop.
This suggests to me that iPhone impacts behavior. Users are much more likely top use it, whereas users of other smart phones are much more likely to favor a few, relatively low bandwidth features.