And I meant in the sense that the MBA won't read email or make facebook posts any faster than the Atom. Tasks like these are what most people do most of the time.
Content creators will want more power, and people running heavyweight apps and clients - the Core series is good for them.
What about people like me who enjoy the occasionnal game of Civilization that runs just acceptably on the power of the MBA, wouldn't on a Netbook. However, getting a MBP or other computer would be overpowered with for my needs.
Face it, the netbook is not enough computer for plenty of people and the MBP is too much. The ultrabook trend packs just the right amount of power, and comes with the portability increase over traditionnal full power laptops.
That is why they are popular.