Can't compare with the 2013 rMPB, but I definitely find that my Air runs much cooler than my 2012 rMPB, even running the same apps. The only time I've ever noticed any heat over the keyboard of the Air is when I'm using it on the couch and have it in my lap without proper space for ventilation. When it's being used on a table or flat surface, I never notice any heat at all.
Hope that helps.