It was released almost 6 months ago. It was announced in October of last year and began shipping on Nov 30th. However it shipped in such limited quantities due to manufacturing challenges with new design elements that it only seems like it was released in early 2013.
This kinda shows up one of the problems in the buying guide's rating system. On their criteria, they're absolutely right. Haswell processors should be coming out in the next few months, Apple will almost certainly do a revision to accommodate them and there's likely to be a couple of other spec bumps too. So if you buy now there's likely to be a better model out in the not too distant future.
However the real question is how much better they'll be and this is where the problem comes in. The big advances with Haswell are expected to be mostly on the integrated GPU that none of the iMac's currently use. Oh there's likely to be a performance increase on the CPU side too but it'll be relatively minor, somewhere between 5 to 15%, and the vast bulk of users won't really notice that if they don't have it. Actually there's a chance that, at least for the basic iMac, Apple will decide to ditch the Nvidia GPU and go with the GT3e instead. This is targeted at the 650m which means all of the 21" models could (in theory) go with the integrated option without compromising on GPU power. Again, most might not notice a difference but those who prefer a dedicated GPU (or like being in Nividia's driver release schedule on the Windows side) may actually end up wanting one of the current models.
This is all speculation of course but it does illustrate the potential downside of the buyers guide. Personally I'd like to see an additional metric based on the likely changes to that product at the next refresh. So, f'instance, the iMac might be looking at minor spec changes while the iPad could get a complete redesign.