It's like with all technology...eventually it will become obsolete. Like XP no longer being supported....gotta buy the new software, then a new computer that will support Windows 7.
One day the 3GS will not be supported....and so on.....
...Xp has no support yet Ms still releases updates for it, unless my Xp machine gets the updates from a MS fake server, Mapple will not update nor release anything for the iPhones, still, 3 years in cellphone world is a lot, even for Nokia or HTC, yet the support for these is better.