I know I've missed special abilities on monsters that would've made a difference. It turns most monsters into running a simple fighter.
That's kind of the catch here. higher CR stuff has more options. For the DM, odds are good it will be the first exposure to those options. So the DM is more likely to forget things.
Some argue the solution is a simpler game, with fewer options, but how simple do you go? When a DM runs all the options correctly, he ends up with a good challenge, so there is value in it. DO you really want to simplify the game, so a 20CR monster is simply a big beast with high AC, BAB, Damage and HP?
I would agree that it would help a DM a lot, for each encounter, to roughly describe the NPC/monster's likely actions/abilities in common situations:
Preparation: if the monster knows the PCs are coming, what stuff does he use to prepare?
Mass Combat: if the monster is facing >4 opponents, what does he do?
Solo Combat: if the monster is facing few attackers, what does he do?
Ranged Combat: if the enemy is at range, what does he do?
Magic Combat: if the enemy is wielding spells, what does he do?
Escape Plan: if the monster is losing, what does he do/use to escape?
Answering those six questions should involve going over the monsters SAs and equipment. Preparation implies utilize any buffs and potions
Escape Plan is you chance to note that the monster has Teleport and will use it.
During the game, you've got to be looking at your answers to those questions (put it on your adventure notes somehow). This should not be a round for round script, simply a note of what the critter can do in each situation. This will REMIND you of what powers the critter has that would apply. You may still miss an ability, but you'll be more prepared and should notice an improvement in your usage of the critter's skills.
Janx