According to Mactrast, a bug in OS X Mountain Lion means it can’t be restored or re-installed on late-2012 iMacs. Attempting to download OS X 10.8 from the Mac App Store will bring up an error stating that it is not compatible with that particular machine (despite it shipping with Mountain Lion).
The problem goes deeper, though, with a similar error message being shown if you already have the installer on your hard drive or SSD and even if you attempt to restore things via Time Machine or the Recovery Partition. The problem appears to affect most Macs built in late-2012, including the new iMac and both the 13 and 15-inch flavours of the MacBook Pro with Retina display.
There’s been no official word from Apple so far on a fix for the issue, but it’s believed that it’ll come in the 10.8.3 update, which has been in the works since November 2012.