Even looking at the 5k iMac, it has a 5k monitor but then only 8gb of ram and no SSD. Have they lost their minds? It's $2500, and it hardly would of cost them more to put an SSD into the damn thing.
Apple is so miserably out of touch with reality here.
You need to spend some time on the Apple store. If you want an SSD the 256Gb is a no-cost option on the retina iMac but, frankly, for most users the fusion drive is actually a better bet. 256Gb will get sucked up very quickly indeed if you're doing the sort of high end video / photography work that screen is perfect for.
Aside from that minor point it's also ridiculously good value when compared with the non-Retina iMac. I was pricing up for one of our labs today and a 3.5Ghz (albeit an i5 rather than i7), 8Gb ram, 1TB Fusion option Retina was about £40 more than the non-Retina!