Yup, gotta love dem telephone-cord cables. From my experience, cables are conveniences rather than necessities. A case in point is Olomana. The steep ridge section just before the summit of the Wailupe middle ridge could be climbed more easily with a well-placed cable. Rappelling is fun, but should be limited to certain areas.
Hawaiian geology makes for very soft and brittle rock.
I've scrambled around a bit on the Koolau summit between Makapuu and Kuliouou, much of the rock in between is extremely crumbly and can pull away in your hand if you put too much weight on it. I seem to recall a story I heard when I was a Keiki regarding some mainland climber types who thought they'd scale the cliffs above Sea Life Park only to fall to their deaths. Thats why the climbers here have only found one rock face on Oahu they will go on. Its near Mokuleia, I never been there, but evidently it is the only rock face they found that is NOT crumbly, NOT suicidal, NOT mossy etc etc. Now a waterfall might have the same charecteristics as the rock at Waimea BAy, or mainland faces.