OS versions aside, there is a major difference between Apple and Google's methods.
Apple has 9 devices total. They designed the hardware, they sell the hardware they write the operating system. It's relatively easy to work in these small confines.
Google on the other hand only writes the basics of their operating system. The specifics of the hardware is left at the discretion of the hardware manufacturer. Same goes for individual tweaks and adjustments of the operating system. These tweaks and adjustments can be further varied by individual carriers and even as far as target markets.
Development and testing for Android will take time to ensure the most widely compatible product possible.