Just my $0.02, feel free to shoot it full of holes...
We know 2012 iMacs have screen lamination issues and are expected late Sept/early Oct.
Lamination is not equal to "retina". It is questionable whether it is lamination or fused panel-glass construct also used in the retina display. That doesn't necessarily mean the pixel density is increasing. Just that the glass and LCD panel are fused together to make a thinner assembly.
2012 Thunderbolt display is likely to be practically identical to iMac screen so they likely have the same issues with it as well.
While likely Apple strongly wants to share LCD panel components between the two, users don't "have to" buy a Thunderbolt display with a Mini. In fact, if trying to control costs then probably don't. The dubious assumption here is that the Mini is one of the primary driver of TB display sales. The TB "display" is primarily a docking station; look at the dangling power cord if have any doubt. Mini don't really need a docking station. There are a
huge number of quality display out there with DVI and Display port inputs that are several hundred dollars cheaper than the TB display. A very sizable number of buyers are going to get (or already have) one of those.
A mini + TB Display costs hundreds more than an iMac. For someone who fells extremely compelled to buy the whole Apple ecosystem it is substantially less expensive to just simply buy the iMac.
The more nature pairings with the TB Display are the two MBA models and perhaps the MBP 13" (and somewhat less so the 15" model). Those all release separate from the new updated TB Display. There is even less motivation to tightly couple the Mini to it.
2011 Thunderbolt display has USB 2.0, old thunderbolt controller and lower res than rMBP
No one is going to buy a rMBP as a "display" for a Mini. The thunderbolt controller difference is immaterial, same speed, same throughput. Since the TB Display is always plugged in the difference in power consumption doesn't matter and the size of the chip has no relevance in a 27" screen sized device. There are going to be other TB peripherals with the old controller too. Apple wasn't selling the old TB Display at a loss either.
Having USB 2.0 on a TB display isn't that bad if primarily going to plug in the keyboard, mouse, trackball/trackpad , etc. (i.e., all of the much slower peripherals ) into those slots freeing up the USB 3.0 sockets for "faster than USB 2.0 speeds" peripherals.
It is "nice to have" have more USB 3.0 sockets, but if plugging in a large number of USB 2.0 devices into the the docking station, then you are really not seeing any increased value there. There are some edge cases where perhaps dynamically plugging in some USB 3.0 device (e.g, newer, faster USB 3.0 flash thumb drive) that is "easier" to get to on the display. But that isn't a "show stopper" issue. It certainly isn't for the 2012 MBA and MBP 13" models.
A coupling to the iMac would be more strongly motivated by some component(s) they do share. For example, a shared discrete GPU option. Even that is somewhat strained because the Mini shares more parts with the MBP 13" .
Up until now it shared overlap with the 'classic' MBP 13". If the rMBP 13" rumors are true, then it may be the case that Apple is now coupling Mini component overlap to that new model. Hence, the Mini won't arrive until the rMBP 13" arrives. For example, the Mini could be picking up GPU, SSD options or other non screen components from that model.
The more likely though is that some other Mac family element is holding it up. Either the Mini is late because it was "lower priority" than the rMBP 13" model or somewhat more sensibly that they are waiting for 10.8.1 to crank volume production of the Mini. In the case of the former, resources were pulled from Mini development to expand the laptop line up. The mini will catch up later. In short, yet another example of Apple not being able to walk and chew gum at the same time.