“The mount is available with all configurations of the iMac and only adds £36 [US$40] to the price of the iMac,” Haslam reports. “Unformtuately this is a CTO option only, so the VESA mount for the 2012 iMac cannot be purchased separately should you already own a 2012 iMac.”
Apple’s website now states: The iMac with Built-in VESA Mount Adapter is ready to pair with your favorite VESA-compatible wall mount, desk mount, or articulating arm (sold separately). This iMac doesn’t include a stand, so a mount is required. If you don’t already have a mount, you can purchase one when you configure your iMac.
Read more in the full article here.