Fanaelialae
Legend
I dunno. If they're talking about maximum-level rogues doing 20d6 damage per round (not even counting weapon and static bonuses), maybe they aren't going to scale back as much as we think.
20d6 is "only" 140 points of damage per round (dpr) before accuracy is factored in (which I'd guess is most likely to be around 66%). So let's assume that accuracy, and weapons and static bonuses cancel each other out such that the rogue has 140 dpr.
4e creatures were designed to last around 4 rounds, but many people seem to consider that too long so let's assume the average (level-equivalent) DDN creature has enough hp to last 3 rounds. That maximum level creature would have around 420 hp.
However, that's assuming that the rogue doesn't have a bit of striker built in, meaning that he deals higher than average damage (at 20d6 per round, I wouldn't call that a stretch). Hence, let's say that what a non-striker can kill in 3 rounds a striker can kill in 2. As a result you'd end up with a creature with 280 hp at max level.
Admittedly not as low as 1e, but significantly lower than 3e or 4e.
Speaking for myself, however, I think it's far more important that they get a healthy ratio and progression between hp and damage, rather than aiming for some arbitrary quantity thereof. As long as the math works well, I don't especially care whether the numbers are big or small.