As 767-400ER and Cedarjet said, many Boeing designs have started out very slowly and almost been termainated, until all of the sudden orders pick up and BAM, all of the sudden they're the hottest aircraft ever. Heck, the 707 started out slowly. And that was when William Boeing was still alive! This is the same thing that both McDonnell Douglas and Boeing were doing ever since the start of the Jet Age. That doesn't show poor management, it's what Boeing has been doing for 45 years, and they have always had success in the end. The 717 isn't selling good either, but orders are picking up. As you know, the 757-200 was the most economical aircraft in the industry, and the 757-300 proves to be even more economical. So here we have a brand new aircraft, which has the potential to be one of the greatest aircraft ever, and people are complaining about it. Its a time-old story. The 737 is only popular with airlines because its cheap to operate and can be used for smaller destinations, earning more revenue. The 753 makes the 737 look like the baby that it is economically. The airlines are hesitant to try a new design for fear of buy something crappy. Once they open their eyes and realized that their grandparents were thinking the same thing with the prototype 737s and 727s, they will star buying. And I assure you, it is not a mistake for Boeing. Realized that this is common for EVERY aircraft company. Lockheed had this with the L-1011, Airbus with the A300. It's NORMAL!! And airlines will also go for the comfortable 767-400ER. You'll see. It's a time-old drama being played out around the world with every product, not just airplanes. It'll work out as it always does.
Soon, the 733, 734, 735, 752, and 763 will all be out of production, and will will have to live with what we got, which is the 737NG, 753, 717, 777 and 764ER.
Then we will realize the importance of these new aircraft.