Once again, this really can't be constituted as a slip-up because it was just a prediction. He couldn't have known at the time of his quote that flying would be possible.
That's like the one guy (I don't remember his name) who said in 1928 that next year would be the end of the Depression, when in actuality 1929 turned out to be the worst year of the Depression.
Of course, there is the possibility that the statement was "politically" motivated.
History tends to paint the Wright Bros. as simple bicycle builders, tinkering away on their own, with little contact with the outside world.
In fact, they were in a race against several groups around the world to become the first persons to achieve powered flight.
So it's possible that the statement was made in the vein of "disinformation", with the desire to make their competitors think they'd given up, or that it was too difficult to achieve.
Without knowing the full context of the statement, it's hard to figure out what might have been going on in his mind when he said it.
Man, give them a break. They were human, and people make mistakes. Besides, do you think that they are some kind of seer that knows what's gonna happen in the future...???
The Wright brothers (Wilbur & Orville) during the first flight, which took place on December 17, 1903 at 10:35 a.m. the aircraft "Flyer" traveled one hundred twenty feet in twelve seconds. Piloted by Orville, the younger brother.
Awwww.... they can't help that. You should be happy you have the right to fly thanks to them. Geez, they thought that b/c it was so hard for them to build a good "flying machine" it would take ages to make one. You know how when you are frustrated doing something, like surfing the web and it takes forever for a site to load, and you say something like, "this'll take ages,"? well, that's what they were getting at.
This would only be a slip-up if they could predict the future. I can predict the future. I predict that Ozzy will continue biting the heads off of small animals.