1. UIKit - Apple made it easy for developers to implement consistent navigation, views, and transitions. Android Ice Cream Sandwich is providing a new UI library which will bring this much needed iOS advantage to Android. Is it possible to mimic UIKit on the current Android devices? Yes, but it's a pain in the ass and not practical for most developers on a deadline.
2. Fragmentation - Device Android version lock has caused problems with development. You are only as strong as your weakest link which unfortunately rings true with some developers who choose to develop on an older version of Android to remain compatible with as many devices as possible. Google has addressed this issue by obtaining agreements from many manufacturers to update their devices on a consistent basis.
3. Screen Resolution - Any web developer will tell you it's much easier to create a beautiful and consistent website if the site is fixed width. This is especially true for mobile development because you dont have to concern yourself with repeating tiles, resolution detection, and adjustable spacing when you know the exact dimensions of the device. There are only 2 iOS resolutions (not counting retina) making it easy to utilize space and perfect the UI in the most efficient way possible. Can it be done on Android? Sure, but without a UIKit to handle many of the little nuances it will yet again be a big pain in the ass and will take up time that the developer does not have.