Well, actually the policy applies at all clubs, however, at 8 Trax, there is a second entrance upstairs that is used for exit and re-entry only. This is mostly because 8 Trax is the only club with ticket pedestals and podiums in two different places. (Contrast that to Mannequins, the only other club that used to have a second re-entry area, but only has a ticket pedestal and podium at the main entrance.) As a result, we have the ability to check your ticket or run your ID through the scanner there, as well. The same rules for ticket and ID checks still apply to the re-entry point. If you were to head to the main entrance to re-enter, you would have to wait in the line. Since the ability exists, the club managers at 8 Trax require the use of the upstairs re-entry to better spread out the Guests inside the club. So it's not so much that 8 Trax is an exception, it's more that it provides another means of getting the job of club admission done.
As for the reason for changing the policy, the response was more of the "straw that broke the camel's back" variety. Underage Guests sneaking into the clubs had been an issue for some time and, over time, many different measures were tried to take care of the problem. Unfortunately, the very nature of the old setup made keeping track of everyone very difficult. The fight was what ultimately led to the club managers to ask for more stringent admissions measures rather than accept small changes.
The liquor license is certainly a very important part of the admissions decisions made at Pleasure Island and I would be very surprised if it didn't play a part in this one. Although bar tenders inside the clubs do not serve Guests without wristbands, they may not think twice about serving someone who has a wristband because they expect the admissions Cast Members outside to have checked the wristband. The new way of doing things better ensures that this check will happen.