That's an interesting graph! The speed is much higher than I expected. I'm not entirely sure it all rings true though, as I was under the impression that in absolute terms rolling resistance was only a handful of watts (see that bicycle rolling resistance website), whereas to do 12mph would require quite a few watts - maybe 100? I just can't imagine rolling resistance being that high. Maybe that is the graph for a really grim set of puncture proof tyres like Marathon +?
I'd heard, and thought it sounded quite reasonable, that at even at 10mph 90% of your effort was being consumed by air resistance (I realise there are other losses, transmission losses etc., but I think these are negligible compared to RR and AR). I have absolutely no data/source to back this up though!
On the other hand, I do feel like the reduction in effort when using a decent set of tyres is easily noticeable, so maybe it is right.
I still have no idea what this has to do with cruising speed.