It's the seams and openings that leak, and they leak because an RV flexes and vibrates a whole lot more than a fixed dwelling. All the joints literally get torn apart. Yeah, many RVs could be built a better to reduce the seam movement problem, but it's still gonna be subject to leaks over time. And Eternabond tape is little better than lap sealant if the seam moves around very much. That said, I would use Eternabond as much as possible if I couldn't get up on the roof to check very often. Properly applied, it covers a wider seam area and is less likely to get cracked open. It doesn't work well everywhere, though, e.g. along complex curves and around small openings like vent pipes.
I've owned rigs with EPDM, TPO, fiberglass and metal roofs and they all leak sooner or later, and near always at those seams and edges. I've had exactly one roof membrane leak, and that was from a low hanging branch on an EPDM (rubber) roof. It ripped a 6" gash and I was immediately aware of it, so it never got a chance to leak.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC