You are partially right. The wide nine scheme is set up by the defensive ends lining up way beyond the offensive tackles, but the point is not to play a "containment" style defense, but rather to attack the quarterback.
The defensive ends are typically smaller and faster than the opposing offensive tackles, so lining up so far to the outside gives the defensive player two advantages. First, he has a better angle to the quarterback and he can use his speed and power to get around the offensive tackle and sack the quarterback. Second, he is lined up so far the the outside of the play that he prevents the offensive guard from coming and double teaming him. The only way that he can be double teamed in this situation is if the tight end or running back stays to block.
Wide nine defenses are typically used in obvious passing situations as the defensive end is only concerned with sacking the quarterback in this setup. This is actually considered a poor technique to use against a running play because the defensive linemen are so far out of position to try and stop a run to the A or C gaps (because the defensive tackles are typically coming through the B gaps to sack the quarterback as well). Also, this play is highly susceptible to the draw play, where the quarterback drops back as if to pass but instead hands the ball off to the running back. This play works because the defensive ends are typically already behind the running back by the time he gets the ball and have no chance at tackling him.
There are two main things that you need to be effective at the wide nine. The first is very talented, fast and athletic defensive ends. The whole point of the wide nine is to get the defensive ends into a one-on-one situation with the offensive tackles and if the defensive end is not able to take advantage of this situation, then there is not much of a point in running the play. The second thing you need is good pass coverage from the defensive secondary. The wide nine is basically selling out to sack the quarterback using only four pass rushers, therefore it can take some time for the defensive ends to get past the offensive tackles and sack the quarterback, so in the mean time the defensive secondary needs to have good coverage on the eligible receivers.
It's also worth noting that the wide nine is far more effective when the quarterback takes a seven step drop rather than a three or a five step drop because it gives the defensive ends longer to get to the quarterback and it gives them a much better angle to attack from.
The wide nine was used heavily in the 2011 NFL season by the New York Giants and the Philadelphia Eagles due to the amount of talent they had at the defensive end position. For more discussion and a video explaining the wide nine, take a look at this smartfootball link.