This article discusses the fragmentation issue of Android phones which refers to the difficulty of an upgrade or the lack of it when updates are available from Google. This is because Google has no complete control on how the Android phones shall be built by each manufacturer which has its own GUI (Graphic User Interface) designs. This is now evident on several Android phones that have yet to get an ICS upgrade while the Jelly Bean is spreading in the wild.
Lifehacker suggest to buy the Nexus instead. Click the link above to read the full article.