There is a lot of time between both designs. The B747 is a fantastic aircraft (I have flown close to 10,000 hours on the classic version).
The Boeing 747 was originally designed for a competition to supply the US armed forces with a large transport aircraft. It lost this competition to the Lockheed C-5 Galaxy. Pan Am placed an order for 25 B747’s and Boeing took a large gamble to further develop the B747. This is all back in the late 1960’s. Although the Boeing 747-400 is a much more efficient version of the original design the basic airframe dates from that time. The Boeing 747-400 is much more efficient than the Boeing 747-200 and 300’s it replaced. Also on the order of 20%. On top of this it reduced cockpit crewing costs because it eliminated the flight engineering position.
The Boeing 777 design date to the early 1990’s. ETOPS was a well established concept, and the resistance that a lot of airlines initially had to flying long haul flights with less than three engines had eased off. This is the case for my airline as well. Even back in the late 1980’s our (then) CEO stated that we would never fly across the ocean on less than three engines. Now it is not even an issue.
The original Boeing 777-200 was nicely slotted in between the Boeing 767 and the Boeing 747-400. So each aircraft served its own niche. But the design of the original Boeing 777 allowed the aircraft to be stretched into the segment served by the Boeing 747-400. All that was required was a very high thrust engine. This challenge was taken up by General Electric with the development of the GE90-115. On the version of the Boeing 747 (-300) I flew each engine produced 52,000 pounds of thrust. The GE-90-115 produces 115,000 pounds of thrust. This new version of the 777 became the Boeing 777-300. A direct competitor for the passenger version of the Boeing 747-400. If an airline already operates the 747 it requires very large capital expenditures to replace them with Boeing 777-300’s. When the fuel prices started to rise the equations started to tilt in favor of this replacement, and that is what you are seeing. Air France is getting rid of their Boeing 747-400 passenger fleet, replacing them with the Boeing 777-300ER (and some A380’s). KLM is taking the first steps in this process, British Airways has also started ordering the aircraft, and in the ultra large capacity segment has ordered the A380. All this will likely mean the end of the Boeing 747 passenger version.
As you know Boeing is in the process of making a new version of the Boeing 747(-8). It only has one significant customer for the passenger version (Lufthansa), it is likely only to see service as a freighter (a role for which it is well suited). But at the moment the cargo market is in a world of hurt, and certainly my airline is not looking for this aircraft.
So, the short of it is that the Boeing 747-400 is most certainly not a bad design. But technology and operating economics (read the huge increase in fuel costs) have changed the playing field in favor of the Boeing 777-300ER for the passenger carrying business.
In my time in the airline business fuel costs have increased from 1/3 of our operational budget to 2/3 of our operational budget (in pure numbers this means a change of one billion Euros).
A shocking number to everyone who reads it for the first time is that as of the end of 2007, the airline business collectively broke even from the time we started to carry passengers/freight/and mail to the end of 2007. That is right not a single Euro/Dollar/Yen was made, in our collective business. The profits made by some, were offset by the huge losses and bankruptcies made by others. This business is extremely silly. Yet “we” were able to make it the safest method of transport over long distances. The losses made by almost everyone since the end of 2007 has only exacerbated this situation.