Speaking as a professional product designer, I say it's real.
I haven't had time to go through all 600 posts so I apologize if I repeat something already mentioned.
First, "not cosmetic" mean it really works. A "cosmetic" unit would look just like a working unit but would be an apperance model. This one is functional and may or may not have the final colors and material finishes. But this one looks like it does have the correct finishes.
Second, the movment of the function key shortcuts has Apple written all over it. Why would a knock off want to piss people off by moving hot keys? That would take re-writing Mac OS software. I beleive someone could physically create a knock off Apple keyboard without cooperation from Apple, but re-map keyboard shortcuts? I think not.
In fact Apple loves to mess with something like the keyboard layout for the sake of consistency. Now they can have the same keyboard layout for both laptops and desktops. The eject key on my MacBook Pro is F13. Now the new iMac will be the same. It's actually brilliant. I love that Apple isn't afraid to offend a few people in order improve ease of use.
As for the removal of the

from the cmd key. Now they can sell this thing to windows or linux users. Again, briliant. Plus the

is just confusing. It's refered to as the command key and its symbol is a cloverleaf. The

part never enters the equation. I too pine for the days when I'd close this window with an "Open Apple - W". But we've all grown up and now it's "cmd-W"
As far as the appearence is concerned, everyone is entitled to thier opinion. I think it's hot. It made me look down at my current wireless keyboard and think "wow, that looks old". Whether it's "stylish" or not (a word I detest) it looks modern, thin, and light. To paint the keys silver would incure extra cost. I'm sure the MacBook Pro keyboard is expensive with its backlit painted and etched keys. The new iMac is gonna have some white plastic on it, so it's gotta match. Plus there is an authenticity to the use of real metal. Having painted keys would ruin that.
All in all, this thing has got me very excited about the new iMac! I am inclinde to believe Apple is allowing these pictures to stick around just to build hype. I mean, who here was worried about the keyboard of the new iMac? It would be like showing the new earbuds for the 6G iPod. A "Cease and Desist" isn't needed but someone is going to get in big trouble.