I figure thinness is secondary. The headphone jack is not controlled by Apple and Apple demands control. It now owns a headphone manufacturer that manufactures devices at very high markups, so why would it continue to permit competition on its devices with other companies?  The adapter will cost enough and be inconvenient enough that it will prevent 3rd party manufacturing of headphones.<p>You say bluetooth, but that requires another battery and is much more expensive to make that a pair of earbuds.  Also Apple is now a top tier member of the Bluetooth SIG, which controls the bluetooth standard and trademarks.  Expect your Extend phase for bluetooth soon.  I personally expect nothing less from the anti-standards anti-interoperability Apple.