Part of the reason why the iPhone is usually a June release and the iPod Touch (and its music-focused siblings) are September releases is probably just necessit

Part of the reason why the iPhone is usually a June release and the iPod Touch (and its music-focused siblings) are September releases is probably just necessity in terms of supply chain management. Launching the iPad in April was very likely a choice to keep release schedules in Apple's mobile unit optimally spaced; we'll likely see an April-June-September schedule for a number of years to come.