I had heard/seen all the facts independently but had never pieced them together until now. I knew that killing the heart with no damage taken could open the way to Sheol before you beat the heart 10 times. I knew that a devil room could open after killing the heart. I knew that since the halloween patch, the only thing in said devil room is a trapdoor that leads down to Sheol (pre-patch you had the chance for a normal devil room). I just didn't realize that that trapdoor was your reward for killing the heart without taking any damage.
Relevant to your question, I assume that's the Devs' way of making you choose between your completion reward and an early trip to Sheol.
"If you save my life, we will rise and shine so bright that the stars go blind and leave the sky." -- Seabound, "Castaway"
Yea I was pretty angry at myself for picking the chest over the devil room after my first mom kill. I still had an extra life and a full health pill on me, and full hearts, and was pretty much maxed out stat wise with brimstone, had 3 flies, an attack fly and steven floating around me.