When it comes to new Apple products, the fact is that we never really know anything for certain until Apple announces it. While the rumor mill is often a valuable source of information about what Apple has coming up next, it's never perfect, and there are always a few things it gets wrong. That said, there are a few solid indicators that can, at times, tell us when Apple has something getting ready to launch. One of the most reliable of these is retailer supply. When retailers start having trouble getting their hands on one of Apple's products, you can bet that a new version is coming sooner than later.
We saw this earlier this year with the Apple TV, and again more recently with the MacBook Pro. Now it seems to be happening with the 27-inch iMac. According to AppleInsider, retailers like Best Buy are beginning to run low on the iMac. The lack of iMac stocks means that Apple is making fewer of them, suggesting that the current model is being phased out to make room for the new hotness.
If you recall the pre-WWDC 2012 buzz, it was widely expected that Apple would announce a new retina display iMac alongside their retina display MacBook Pro. That, of course, didn't happen, prompting speculation that it would be coming either later this year or next year. While Apple confirmed that the Mac Pro would be getting an overhaul in 2013 and that the iMac would be getting an update, they declined to say when the new iMac would be launching. A later report suggested that a new non-retina iMac would be coming later this year, while another (probably less reliable) predicted that the new iMac will, in fact, have a retina display.
The iMac is definitely in need of an update. The current model has been left untouched by Apple for over a year. While the inclusion of a retina display in the update is still up in the air, it seems clear that those wanting a refresh of Apple's popular all-in-one computer are about to get their wish.