First off, they're circles, not levels.
People like Diablus blatantly lied because if you've ever read Dante's Inferno, then you're probably a Catholic(like myself) and you'd know that anything you do is horribly sinful (like using birth control for example). Additionally, with all of Diablus's talk of action and getting ass, you'd expect him to atleast be placed in the second circle (for lustful people).
Edit: Ok, I took the quiz
Second Circle of Hell
You have come to a place mute of all light, where the wind bellows as the sea does in a tempest. This is the realm where the lustful spend eternity. Here, sinners are blown around endlessly by the unforgiving winds of unquenchable desire as punishment for their transgressions. The infernal hurricane that never rests hurtles the spirits onward in its rapine, whirling them round, and smiting, it molests them. You have betrayed reason at the behest of your appetite for pleasure, and so here you are doomed to remain. Cleopatra and Helen of Troy are two that share in your fate.
Like I said, strict Catholic views regarding sex = damnation. Oh no, I've had sex before marriage, and I've masturbated/viewed porno before like 99.9% of the male population, eternal suffering is mine! Too much info? Too bad.