There appears to be some misperceptions on the part of Kanex about what is really occurring for the 27" iMac. Or, they are being purposely dishonest. You will find a hint of their misunderstanding in the note about the 24" Apple LED Display.
Apple created the 27" iMac with Target Display Mode for folks to be able to use the display with other Macs that have DisplayPort signaling; MacBooks, Mac minis, etc. When the iMac is in Target Display Mode the video signal from the external DisplayPort source is routed directly to the iMac's display, it does not pass through the iMac's GPU. The display is being driven by the external source's GPU, which is not a problem when the external source is another Mac with DisplayPort signaling.
The issue is that folks are wanting to connect external devices that are not sending DisplayPort signals, so they are putting this adapter from Kanex in the connection to convert their device's native signaling to DisplayPort. The native resolution of the 27" iMac's display is 2560 x 1440. These external devices, such as an XBox cannot drive that resolution, but they can drive 720p which is 1280 x 720, exactly half of the iMac's display's resolution. So the signal just doubles the pixels on the iMac's display.
But the Kanex converter does not have a GPU to drive the alternative devices resolutions, which is why it cannot be used with the 24" LED Display. The only way for Apple to provide 1920 x 1080 resolution is to crowd a second GPU for the external sources into the iMac. That is not something that I think that they will do. They made this Mac to work with their other Macs, which it does, right out of the box, with no extra converters.
Dah•veed
