Put a new coat of paint on it and some of those who bought the earlier one and love it will "upgrade".
Improve on an issue that was holding potential owners off from buying - they will now buy it.
Refresh something that was a scary price for people half a decade ago - on their current income it's not so scary - they will buy it.
Show it to a couple of high profile forum posters with zero hype, promises or specs - all the umming and ahhing will be done prior to the announcement/release date etc - speculation and drooling will be sorted - pre-orders are guaranteed.
note: am probably going to buy one now - while the original HD800 had been an out of reach, never to happen dream. The bundling of the balanced cable will also drag me into the amp at least - probably the DAC too. The refresh has definitely made me look at the product again... and think - "I could actually own one now". Am tipping that I'm not alone in finding that their wallet is a bit more padded than it was when the headphone originally came out and they made a decision to never pay more than $xxx for headphones. The realisation that I can now if I want to is a huge hurdle that's been jumped.