Can't install Mountain Lion on late-2012 27" iMac...

I just got a brand spanking new late-2012 model of a 27" iMac at work.  Since I like to do clean installs of the OS no matter what the platform, that was the first thing I tried to do.  I can't easily do the Internet Recovery thing because that doesn't work through my company's firewall.  So I tried to download Mountain Lion from the App Store.  It didn't let me because it said Mountain Lion is not compatible with my machine, even though it is already running Mountain Lion (10.8.2).  Weird.

So I go home and buy a copy of Mountain Lion from the App Store on my Mac Mini.  I make a bootable USB stick from it and bring it into the office.  I tried booting the iMac with it, but when I do I just a grey "prohibited" symbol for a few minutes and then the box shuts off.  I then reboot the iMac into the copy of Mountain Lion that's already on the machine, and try to manually run the Mountain Lion installer that's on the USB stick only to be greeted with the same message I got when I tried to download it from the App Store: Mountain Lion is not compatible with this machine.

Anybody have any idea what I'm doing wrong?  I guess I have no choice but to try the Internet Recovery method.  It's a pain for me because I have to hook the box up directly to the Internet, but I think I really need to know if it'll work or not.  I'm thinking it *has* to work; if not then something really messed up is going on.

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  • New machines that were released after the last build of Mac OS X usually have a specific build of the operating system, usually new hardware drivers that have made their first appearance in that model. The drivers will eventually be added to the mainstream version of the OS in the next one or two combo update releases. Until then, internet recovery through the recovery partition is your only option.
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