Generally speaking "12+ hours" means "basic browsing" or watching a movie which can be natively decoded with the built-in video processor. I don't think that includes any serious workload (tens of tabs open and any kind of developer/creative workflow). New Intel processors have greatly improved idle battery life, but "working" battery life still requires the watts.

In Apple's case they are reducing watts and presuming lots of idle time. This may match a large number of their users - I only hear complaints from developers.

EDIT: watt-hours? Sorry, my electrical knowledge is not awesome.