Also, some monsters were given extensive changes which included CR. For example, compare:
3.0 Nalfeshnee; Huge outsider; HD 11d8+44; Init +1; Spd 30 fly 40 (poor); AC 28; Atk Bite +15 (2d4+6) and 2 claws +13 (1d4+3); SA Spell-like abilities, summon tanar'ri, smite; SQ DR 20/+2, SR 24, Tanar'ri qualities, know alignment, see invisibility; SV Fort +11 Ref +8, Will +13; AB Str 23, Dex 13, Con 19, Int 22, Wis 22, Cha 16; Feats Cleave, Multiattack, Power attack; CR 16.
Smite does 15 points of damage in a 60 ft radius and forces a Will save (DC 18) or make people be in "stupor" for 1d10 rounds. Spell-like abilities: At will-alter self, call lightning, chaos hammer, chill touch, death knell, deeper darkness, desecrate, detect magic, feeblemind, forget, greater dispelling, invisibility (self only), magic circle against good (self only), mirror image, raise dead, slow, teleport without error (self plus 50 pounds of objects only), unholy aura, unholy blight, and web. These abilities are as the spells cast by a 12th-level sorcerer (save DC 13 + spell level). Their summons work twice per day, and either have a 50% chance of getting 1d4 vrock, 1d4 hezrou, or 1 glabrezu, or a 20% chance of getting another nalfeshnee.
3.5 Nalfeshnee: Huge outsider; HD 14d8+112; Init +1; Spd 30 fly 40; AC 27; Atk Bite +20 (2d8+7) and 2 claws +17 (1d8+3); SA Spell-like abilities, Smite, summon tanar'ri; SQ DR 10/good, tanar'ri qualities, SR 22, true seeing; SV Fort +17, Ref +10, Will +15; AB Str 25, Dex 13, Con 27, Int 22, Wis 22, Cha 20; Feats Cleave, Improved Bull Rush, Multiattack, Power Attack, Weapon Focus (bite); CR 14
The Smite ability no longer deals damage, but has DC 22 and dazes people instead of putting them in a non-defined "stupor". Their spell-like abilites have been reduced to: Call Lightning, Feeblemind, Greater Dispel Magic, Slow, Greater Teleport and Unholy Aura. Summons are the same.
So, +5 to hit, double base damage before Str, more HD and a much bigger Con leading to tons more hp, replace Know Alignment and See Invisible with True Seeing, and some reduction in spell-like abilities that probably didn't see much use... and a Challenge Rating that's two *less* than before.