NEC makes no mention or requirement of insulating staples for NM cable (Romex). Further, it makes no mention that said staples even be a listed product. Of course if it is listed, it must be used in complete agreement with it's listing, but it need not be listed.
That's NEC however. Local laws vary a lot. The whole east coast of the US (at least the part North enough to have basements) is bound by some unspoken agreement that if we ALL wire our basements with romex stapled to the sill plate, they can't come after us all.... Anywhere else they call that unprotected........ So local customs ("the way it's done around here") is probably one of dozens or more ways of complying with the code, but it just sorts it's self out to a common way, stores stock common hardware, electricians know just what to do when they look at a project, inspectors can just check the boxes and don't have to drag out the good book for every box and fixture in the building....
Personal opinion... It's a staple. It's going into wood. If the cable is not damaged during the installation, is snug under the staple, and supported often enough.... (They're usually supported more than necessary for aesthetics if they're exposed), then job done. If the cable were to get hooked on something (then it's unprotected, but I digress....), if it got reefed on enough to damage the cable and contact one wire, you still don't care. It needs replacement if it's damaged, even if there's no "symptom". If it touches two wires, that's what breakers are for, and what they excel at. Instant snap, no heat, no fires, no nothing... Everything works as it should. And the wire needs new either way. I wouldn't loose any sleep over it at all. Well, I'd loose sleep over exposed getting pulled on in the first place. There's a couple of annoying rules to it, but conduit is your friend in a working area. Under a wall though.... No worries.
