Not only does 4.3 bring with it some of behind the scenes updates, it also allows those 2 HIGHLY popular devices the opportunity to pair with the new Galaxy Gear. (Samsung's really hoping to push that for Christmas... and at 800,000 units sold when it was only good for one device... just imagine).
It also brings with it the KNOX software (so you can be sure your email's secure).
No word if the generation prior will also get this update, but it's doubtful.
For more firmware update timelines, check out our database page (or see the chart embedded below).