It's a semi-successful attempt to get tickets into the hands of the fans that are willing to put forth a little extra effort to see their favorite bands. Yes, passwords are inevitably released, but apparently this one wasn't all that easy to get, based on the number of requests in the other thread. Even some of the well-informed regulars here seemed to miss it.
It's not a perfect system, but it's usually much easier to get tickets via the presale than it is on the regular on-sale date. You just need to do your research and start clicking at 9:59am. With a few exceptions, that'll work almost every time.
Without the presales, you have to fight with everyone else who saw the big ad in the City Paper, heard the radio announcements, check out every show that goes on sale every Thursday, and all of their friends who they called to tell them the big news.
Presales rule.