PAXboy is right of course - Boeing is using the 6000ft cabin altitude as a means of differentiating the Dreamliner from "ordinary" airliners (including - ironically - their own)
But let's also remember that Airbus - after a lot of hesitation - are now on the same path with the A350 XWB which will also offer 6000ft max cabin altitude - and 20% humidity..
Soon all airliners will be like this. It'll be like jets versus pistons. The 6000ft cabins will win. 8000ft airliners will collapse in value. The cosy assumption that a well-maintained 747 could fly for 30-40 years will be shown up as just plain wrong. Sure it'll still fly just fine - but no one will want to fly in it. Watch those 8000ft cabin seat-prices slide and those used aluminium aircraft residuals start to crumble.
The days when passengers had no option but to endure being reduced to a semi-comotose state of virtual anaesthesia at the fag-end of a long-haul could be coming to an end sooner than we all think.
Of course this is isn't going to be popular with traditionalists and knuckle-dragging neanderthals - and it's certainly going to be traumatic for the aviation industry. .....But it will be good for passengers and good for pilots.