Hadn’t thought about that before. I thought I had just seen it explained like my previous post elsewhere on the forum though I don’t remember where now…
Found this from Normis
All switched ports share 1gbps full duplex link to CPU, other than that there should be no difference
in this thread
http://forum.mikrotik.com/t/ccr1009-8g-1s-1s-general-info-questions/76651/1
Looks like my explanation was wrong…