I've done a lot of decks using natural wood (cedar, Ipe, treated, fir). The one common factor with all wood on the flat is that eventually they will crack and the grain will lift. In the case of splintering, I wonder if that person was referencing grain lift? I've not personally seen a deck with splinter, but I have seen plenty with grain lift.
I always tell people that all wood is like our skin. To keep our skin from deteriorating prematurely, we need to use lotion and sunscreen. Anything made of natural wood and exposed to the elements needs to be treated the same way. I like products like Sikkens. They dry slower, which to me means they penetrate better, but nothing is going to be a magic bullet treatment for natural wood on the flat exposed to the elements.