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One bonus nobody has mentioned -- you can change screen resolutions and they are all sharp!
From a distance, if you look closer you'll see a bit of fuzziness. Keep in mind that changing the resolution also changes the DPI thus fonts will be smaller and more difficult to read. On a notebook this doesn't matter all that much because it is much closer to you. On a desktop it can be the difference between able to read and not able to read.
 
I requested a CTO model and it took 2 weeks to arrive on my desk. So far I checked the Apple Store edu site and saw a couple Retina iMac orders for the school. However, I'm the first in this campus to have a Retina iMac. :D

At home, if didn't have a 13-inch rMBP (mid-2014) and 27-inch Apple LED display, I would consider the Retina iMac. It is such a beautiful desktop to use.
 
I asked at our local computer store and the salesman said the Retina iMacs are not big sellers. They had plenty of base models in stock, discounted $100.

I think the biggest factor is that most people have a desktop that's "good enough" and the retina screen is not a must have attraction. The higher end BTOs may be doing better, as it's more suitable for serious photo and video work. Apple should get these in stores.
 
It probably all comes down to the price tag. This thing starts at 2500$ and if you do some upgrades you easily exceed the 3000$ mark. The 15" MacBook Pro Retina with the dedicated GPU probably won't sell that much for the very same reason. And the same can be said for the Mac Pro but it is aimed at quite a different audience. Probably the normal iMacs and the MacBook Air are the high sellers but they have a much lower price tag.
 
Getting the riMac with the education/military discount is a no-brainer. I work for the government and always use the discounts. I have purchased my last 3 iMacs using the discount on the Apple website and Apple has NEVER checked my credentials. Makes me think that just about anyone can order with the discount. Heck, the worst Apple can do is say no so what the heck. Why not try.

On my riMac order, the discount chopped about $500 off the purchase price.
 
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