You actually have to look at Nokia's numbers, though, to understand why. The global smartphone leader by a huge margin, its marketshare shrank from 63.3 percent to just 43.6 percent. So, not only did it lose 20 percent of its grip, its marketshare fell below 50 percent for the first time in several years, according to Needham's chart. And, more to the point, its drop is roughly proportional with the iPhone's rise in the last quarter. In fact, the iPhone is the only reason smartphone growth did not slow overall. FWIW, RIM and Windows Mobile's marketshare stayed roughly constant, dipping slightly.
Even though it's not like the iPhone is stealing Nokia's users directly—many of the iPhone's are first-time "smartphone" owners in the US—it does make it painfully clear how unwise it is for Nokia to essentially forego certain segments of the market. Hey, guess who their flagship N97 precisely doesn't target? [Cult of Mac, AI]