According to a new post by Marco Arment of Instapaper, the 2012 iMac will be coming with Ivy Bridge processors and USB 3.0 but, perhaps unsurprisingly, without a retina display.

I’ve now heard from multiple sources that while an iMac update is indeed coming this fall, it will not have Retina displays.

While Apple’s long-term strategy clearly involves incorporating high-resolution displays in all of its devices, from the iPhone to the iPad to the new MacBook Pro lines – there are several reasons why it’s too soon for a 27″ iMac retina display.

While the iMac is inherently a more expensive product, and with less pressure on margins compared with the super-competitive 13″-15″ laptop market, Apple only actually updated the one 15″ MacBook Pro model and left the rest of the range with standard resolution displays. The 2012 15″ Retina MacBook Pro is Apple’s Rolls Royce product – and has a price-tag to match.

It would require production capacities and yields greater than Apple currently possesses to produce a 27″ retina display for an iMac. And 27″ translates to a mind-blowing resolution of 5120 x 2880 pixels, and that kind of resolution is, at this point, several years ahead of the software required to make full use of it, or indeed the consumer demand to justify its production.

While Apple have already created “retina ready” versions of their most popular native apps (Mail, Calendar, iMovie etc), it would be unlikely that Apple would make the necessary investment in creating an even higher resolution version of each app for the relatively small iMac market at this point in time.

While a scheduled employee store meeting had spurred hopes that the 2012 iMac would be announced this week following the WWDC Mac updates, all signs point towards a Fall release.