Hmm, I'm gonna say "yes and no" to that second paragraph.

While, yes, the sealing technique was used to save the village, as we've seen from when the 3rd used the technique on Orochimaru, it can also be used to simply kill the target. Obviously though the 4th didn't have to take Kyuubi to the underworld with him. He instead sealed it inside Naruto, for the good of the village. Or for the good of Naruto. One of the two I'm sure.