An rng system without low rng won't do much to keep people playing, so it's an entirely natural caveat to make, if one that doesn't need to be explicitly stated. I personally can't even think of someone that doesn't equate rng based systems with low rng. As for the analogy, exp in a system when levels are obtained at random are completely arbitrary. The crux is that the progression is locked behind an RNG wall, which isn't something everyone enjoys. As for frequent small upgrades... what's the difference between tomestones and your suggested high rng system, besides forcing players into content they might loathe doing for the sake of a 1 in 10 chance to win a bit of progression?