It was perhaps worded poorly but that's not what the article said: "Dreamliner will use 20 percent less fuel than jets of similar size…" I would wager a lot that if a 777 was redesigned with composites it would likely have similar fuel savings (~20%) over an aluminum 777.
If you take a look at the table in the link at the bottom you will see the 777 is primarily for long-range, high-capacity flights. The 787 was originally intended as a replacement for the 767 and as a competitor to the A330-200. The majority of flights are shorter and carry fewer passengers than the target of the 777. So fuel efficiency is just fuel efficiency and fewer passengers is just a different market segment. The 787 is simply aimed at a different and higher volume market than the 777.
http://en.wikipedia.org/wiki/Competition_between_Airbus_and_...
The difference between the 380 and 787 were the markets that were trying to buy them. The 380 made good sense for UAE carriers because Dubai is trying to be a hub between the east and west. The airlines in the west and east don't want their roles to be diminished so they see the 787 as a point to point airplane. No hub or refueling stops necessary.
After having to deal with Atlanta, Chicago, Charlotte, and Heathrow I'd much rather get to my destination than have to deal with another hub.