Because Apple is a consumer product company that makes money based on change. Forcing you to update makes them money.
And Apple has been doing this for a long, long time. Even before the iPhone. The original iMac came without a floppy drive. Users were angry.
Apple cut off support and security updates for OS X 10.5.8, despite the fact that there is a small but very much alive community of PowerPC enthusiasts (of which I am part). Apple continues to slowly dismantle protocols and products and services that we use. All in an effort to force us, finally, to upgrade to Intel Macs.
It shouldn't matter what we do with old devices or what systems we want to run on them, but Apple wants to control the experience and it wants to keep everyone together at roughly the same level. Again, forcing people to move forward means more sales for Apple.

Stupid capitalism!
Thanks though for the great information as always eyoungren