Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
iPad's Orientation Lock Switch Becomes Mute Switch With iOS 4.2
System controls on multitasking tray in iOS 4.2 beta for iPad showing screen orientation lock
One of the text notes accompanying AppAdvice's video walkthrough of the new iOS 4.2 for iPad suggests that the physical switch on the iPad's side for locking the screen orientation has been repurposed as a mute switch. The change has been confirmed by posters in our forums.
With the change, screen orientation locking is now accomplished within the multitasking tray as on the iPhone under iOS 4. Interestingly, the switch had been originally planned to be a mute switch but was repurposed as an orientation lock as revealed in publicity materials published just weeks before the device's launch.
iPad external buttons and controls: originally-announced (left) and as-released (right)
It is unknown whether Apple had originally planned for iOS 4 to be available for the iPad in time to its initial launch so as to support multitasking tray-based screen orientation locking, or if the changes over time have simply been adjustments to fluctuating priorities and development of new software solutions for certain tasks.