Your Tweet woke me up!
As I said on Twitter, I think that is BS.
That story doesn't have *any* actual sources at all. It's simply reprinting an
unsourced story from Product Reviews, which MacWorld classes as "a new report suggests".
If you look at the article at Product Reviews, it has nothing to back it up at all. It's all assumption, speculation, and hope.
"it is also a sure thing for Apple users to see a new Retina iMac soon."
"It stands to reason that the next upgrade, way before we see a 6th generation iPhone, will be a Retina iMac with standard SSD and even a combo hard drive option considering it’s a desktop."
That's worse than basing an article on nothing but a "report" at DigiTimes

This seems to happen with some of these sites. Rumours reinforce rumours, with nothing to back them up. One site will print something without a decent source, a second site will re-print it, using the first site as a source, and so on.
I do think a Retina iMac will happen, but nothing I've seen anywhere else makes a decent case for it happening this year. Display yields would be a big issue, and of course cost. Once it does happen, I wonder if - initially - Apple will keep the normal iMacs, and release a Retina iMac above them (just as it has done with the MBP). Then the next year or so, when prices are better and software has caught up, drop the non-Retina altogether...
The most logical claims I've seen so far for the delay in a new iMac have been regarding GPU availability.
With the 15" MacBook Pro, Apple has switched from AMD Radeon to one of the new GeForce Kepler GPUs (the 13" and both Airs just use Ivy Bridge's onboard Intel HD graphics). So, it would make sense (you'd think) for Apple to also switch its desktop line from Radeon to GeForce.
GeForce's new Kepler architecture is apparently more of a jump (in GPU) than the CPU architecture going from Sandy Bridge to Ivy Bridge.
If Apple is switching the iMac to GeForce, the high-end mobile card that uses Kepler, the one that would be a good match for the high-end iMac, isn't going to be available until at least the end of June.
So the speculation is that Apple is waiting for that, before then spec-bumping the iMacs with Ivy Bridge, USB 3, and GeForce GPUs.