Hey all!
The hit point formula is pretty straightforward.
Level +1, x Role Hit Die Modifier*, + Con Score, x Power Hit Die Modifier**
*Role Modifiers:
Brute = 10 hp/level
Soldier, Skirmisher = 8 hp/level
Artillery, Controller = 6 hp/level
I forget what the lurker is, sorry.
**Power Modifiers
Minion = Unknown yet, 1/4 would seem appropos, but I don't know if that fits.
Elite = x2
Solo = x5
The reason the Pit Fiend is probably so far out is because it pays for extra summoned monsters with its hit points.
The Skeletal Tomb Guardian is way out, but there were lots of flaws in its write-up.
Most of the others (non-DDM) work out exactly.
It also seems likely the dragons will scale up (no pun intended) 10 levels per age category, with an age category also an increase in size.