I think part of it has to do with the fact that they market one product (iphone) and they market that one product well. It seems like there's a new Android based phone every few months/sometimes weeks, so no phone lasts long enough to make any kind of impact. Android phone manufacturers are constantly flooding the market with new products resulting in a lot of generic sounding products that fall from the public eye in a flash.
People make a big deal out of each new iPhone because they know it's going to be the premier ios product for a good while. If ios had the iPhone 5, iPhone 5 4g, iPhone 5 Epic, iPhone 5 Galaxy Touch, iPhone 5 Xtreme Galaxy Touch II Xtra Xtreme!! edition all released within a few months of each other, each particular phone would generate much less interest individually than one significant upgrade would.
Not saying things should change, as I know Android manufacturers are in a constant game of one-upsmanship to have the new big Droid. Just giving my thoughts on the situation.