When Apple gave their WWDC 2012 keynote two weeks ago, they talked about all sorts of new products – updates to the MacBook Air and MacBook Pro, a retina display MacBook Pro, iOS 6, and OS X Mountain Lion. Most of what they talked about was what we had expected. There were a few things, however, that Apple didn’t announce. One of those was a retina display update for the iMac. Several reports prior to WWDC suggested that the iMac would be getting a retina display, but Apple remained quiet about the topic.

Within a week, they had confirmed that we would be seeing major updates to the iMac and the Mac Pro. Yet there was no mention of a retina display. Now it looks like there may be a reason for that: it seems that the retina display won’t be making the jump to the iMac for quite some time yet. Though there does appear to be a significant iMac upgrade on tap for 2012, the retina display won’t be coming until sometime in 2013 (possibly at WWDC).

According to Marco Arment, developer of Instapaper, new iMacs will be coming in the fall, but without the retina display. Arment posted to his blog on Friday about the features he was expecting to see in the new iMacs. He suggested that only one retina display MacBook was announced at WWDC because the retina display technology is still too expensive to roll out across the board, especially considering that many of Apple’s MacBook customers are students. The iMac, meanwhile, is more of a family computer, which means a fall release (i.e., just in time for the holiday shopping season) makes more sense.

In response to that post, Arment was contacted by “multiple sources” who confirmed that an updated iMac will be released in the fall, but that it will not have a retina display. Though these sources apparently didn’t say that a retina display iMac would be coming in 2013, it seems likely. As Arment points out, Apple is betting heavily on retina display technology. They’ve added it to their two main iOS devices – the iPhone and the iPad – and begun bringing it to the MacBook lines as well. As the cost of retina display tech drops over the next few years, you can bet that we’ll be seeing retina displays on every Mac with an integrated display. In fact, it’s a fair bet that we’ll eventually see a retina display iPod Touch, retina versions of Apple’s Cinema Displays, and maybe even retina displays on smaller devices like the iPod Nano.

Unfortunately, a total rollout of retina displays across Apple’s whole lineup is likely to take several years. Which means that if you’re holding your breath for a retina display iMac, you’re going to have quite awhile to wait.