Thanks for reporting it. As per section "Device Parameters", if you calculate the peak read bandwidth/Processing Element for register and LDS for Pitcairn XT (which is based on GCN), the numbers come as follows:
Register Peak Read Bandwidth/ Processing Element = 15360 / (1 * 1280) = 12B /cycle
LDS Peak Read Bandwidth/ Processing Element = 2560 / (1 * 1280) = 2B /cycle
But the numbers seem okay for NI or Evergreen.
So, indeed the numbers look confusing for GCN [at least term peak read bandwidth/Stream core for GCN]. I've asked someone for more clarification and forwarded a request to update, if required, the corresponding sections of the guide. I'll let you know as soon as I get any reply.
We are in the process of updating the user guide, and will ensure that the table listing the bandwidths is updated.