I think you may be missing the important point, here. With the iPhone there's one manufacturer and each new model is designed to be an upgrade from the previous model. In other words, there's only one product line for the iPhone. There is now two for the iPad (regular and mini) and four for the iPod (shuffle, nano, touch and classic). With Android there are several manufacturers all putting out new versions of phones on multiple product lines. Given that they only release one new phone on this one line every 10-12 months, and that it's an objectively awesome product, it's easy to see why there's so much buzz for each release. Everyone who wants what will be the best iPhone for the next year is waiting for the exact same date and time. Which Android phone is the "best" is much more subjective and will change every couple months. There isn't a huge backlog of super devoted fans all waiting to get their hands on one product all at the same time. The S4 has been the closest thing to that since the original Droid debuted at Verizon and even then there were two phones being released simultaneously with almost no fan base.
I think that that fact, along with the tradition of waiting in line for each new phone are the main reasons you see it with iPhones but not Android phones.