It's most notably a carrier-influenced result, where Android is available for Verizon, Sprint and T-Mobile, in multiple flavors, with heavy subsidies, including "free" phones. I would expect given the same forward momentum, Android will overtake the RIM OS as number 1 in the US at some point in the future.

iPhone as a product should still be able to do well when compared to individual handset models from others, but I don't think it can keep Android at bay in sheer all-model device numbers, especially when limited only to the AT&T network. This is likely only to change with the rollout of 4G technologies, because we're not going to see a CDMA iPhone.

Android is most definitely eating away at the share of dumber devices as well. Luckily many of the manufacturers of such devices are now shipping Android phones, so they're still able to maintain/grow market share. I think the companies who should be most worried about this news are Nokia and Microsoft.