I think people are getting ahead of themselves saying the desire is "better" than the iphone 4, sure it's a lot better than the 3GS, but hardware wise alone the iPhone 4 is the better phone, but there are other android devices out there like the Galaxy S, Xperia and EVO which offer the same kind of clout, if not more.
I think the main reason is OS preference alone, I'm also in the camp of Android lovers, as I said above it's hard to get excited about a device that has basically the same interface it had 3 years ago and 3 years in the mobile industry is a long time. It's also easy for an Iphone owner to get excited about features they haven't had before like "Multitasking" which android owners have had from 1.0, OS wise they're just not bringing anything new to the table for android owners.
I also understand that they have come at it from a different angle to Google, and that's ok, Android is a lot more customizable and feels like more of a smartphone OS than the iPhone OS, which still feels very phoney, if that makes sense and though the iPhone may be fast and reliable it's hard to take a step back from the freedom Android offers to the interface apple offers to you.
Interface customization alone is one of the greatest features that Android offers, it may seem like a small thing to have and maybe it is to some, but to be able to make your device work and look the way you want it is great. Listen to that iPad announcement video from the apple website, even they use the sentiment in their sales patter: "I don't have to change to fit the device, the device fits me".
Hope that all makes sense.