Well, it never officially did. From the Macintosh Garden page I linked:

> Despite Apple's claim that the SDK was available for Intel Macs only, some clever developers soon realized that all the frameworks and programs the SDK delivered were compiled as Universal (PPC/Intel) code while the compiler configuration files were ARM/Intel only. Moreover the installer checked for Intel architecture and denied installation on PPC Macs. Installing the .pkg archives manually and repairing the compiler configurations made the iPhone SDK run completely on PPC Macs.