I'll admit to being guilty of taking "rolling boil" too literally, as well. I use a converted keggle, and only do 5G batches. With a rockin' and rollin' boil, I was ending up with <4.5G in the fermenter, and my hop filtration setup is pretty efficient. I'd end up sparging more to try to offset this, but for whatever reason--probably my kettle physics along with the flame being too hot and high--I'd still end up short.
A few months ago, I finally had the opportunity to join another homebrewer in a brew session. He had his burner turned down so low that there was barely a simmer breaking on the surface. There was still boil off--no question about that--but I argued politely with him using the conventional wisdom that a rolling boil was needed for all those wonderful chemical reactions we count on to create beer magic. He just shrugged and said that's what he'd always done and had no issues. I bit my tongue.
On my next brew day, I thought that I'd just see what would happen if I backed off on the flame. I'm never that accurate with my volume measurements--"close" is good enough for me--but I was a little more diligent this time. Sure enough, I got boil off, and this time I actually wound up with my target 5 gallons in primary. I still got hot break, and good hop extraction, and the concentration of flavors, plus I probably used a lot less propane (this is subjective, but my 20# cylinder is lasting for quite a few more brew sessions now). That's a lot of wins, if you ask me.
My grasp on chemistry and physics and thermal dynamics is tenuous at best, but the important thing I took away from this is that the wort doesn't need to be boiling (or at least boiling hard) for evaporation of water to occur. Boiling, and the degree to which the boil is vigorous, just accelerates that rate. Mind you, that's simply observational evidence and not empirical.