Gnolls have darkvision, +1 nat armor, and a 15 str. That's all they have going for them. Yet, at 2 HD, they're a CR 1.
So 2 HD Gnolls have 11 hp, a 15 AC (including a shield they can't actually use with the spear they're two-handing, so really 13 AC), and +3 to hit with a spear for 1d8+3 (or +2 power attack for 1d8+6).
A 1 HD Half-Orc fighter gets darkvision also, but using the NPC array she has 13 hp (14 con, favored class), a 16 AC (scalemail, 12 dex), +5 to hit (17 str, weapon focus) for 1d8+4 or power attack for 1d8+7. And that's with only medium armor and a simple weapon. Fighters get heavy armor and martial weapons. And full BAB. And more feats.
So is it just me, or does the CR 1/2 fighter completely pwn the CR 1 Gnoll in every way? Better stats, more feats and skills, better proficiencies, better BAB. Yet for some reason the Gnoll is a higher CR.