Except I've seen the exact opposite in my Zul runs. With more people who are geared and who are familiar with the mechanics of the dungeons, it's been several weeks since I had a failed run, or even a run that took longer than half an hour. And I know the exact opposite end of the spectrum too: after 4.1 hit, I could never get a group who could finish a run, and those that did tended to take a few hours with numerous wipes in the process.

The queue time for the Cataclysm heroics have gone down, yes...but it's been because the gear from the Zul heroics and then 4.2 gear made them much more manageable. For many of us, the Zul heroics are already getting to that point of manageability, and once 4.3 hits that will be true for a much wider range of people (nerfed Firelands, the Hour of Twilight heroics and then the LFR gear drops will all ensure that picking up 378 gear will carry much less stress). A group wearing a mix of 365 and 378 items could nearly faceroll the majority of ZG and ZA. Example: the Nalorakk trash pulls that contained Witch Doctors used to require atleast one CC or a wipe was almost guaranteed. Now I've had PuGs who could just burn down those groups without much difficulty.

There are two things you're forgetting when you make the comparison to Oculus and Halls of Reflection. First, people dropped from Occ due to the increased complexity of just finding your way around, not because the fights were hard (in fact, it was probably one of the easier of the 80 heroics). Eregos could give some people problems, but once you figured out how to use the drakes, it was fairly straight-forward. (Except for the Planar Shift, people seemed determined to face-tank the orbs he summons...) Second, Halls of Reflection was very brutal and unforgiving even with ICC gear; the rush of mobs in each wave and the tactics to kill each one more easily were difficult to handle even for the more skilled players.
The Zul dungeons don't suffer much from either problem. Sure, Jin'do still confuses some people, and pulling adds in ZA can lead to a wipe, but they're nowhere near as complex or tough as Occ or HoR, and they'll only get easier once 4.3 rolls around.

I think all of these people raising concerns about PuGs disbanding as soon as they see the ZA or ZG loading screens are being a bit preemptive. Sure, they can be a bit longer than the Cata heroics, but we'll be able to blaze through them just as easily with all of the new gear we'll be getting.