It's interesting that a third party designer
ran the numbers and found that by 30th level, players are missing +5 to hit.
He didn't take into account many other game mechanics such as synergy bonuses from other PCs.
For example, a Cleric that gives a +2 to hit bonus with Righteous Brand at level 1 might be giving a +4 or +5 bonus to hit with it at level 30.
Many PCs can slide foes into flanking positions (or shift themselves into flanking positions) a lot more often at high levels.
Some PCs have up to 4 defenses they can attack. By level 30, it starts to become obvious (minimally via Monster checks) which defenses might be lowest. And many higher level creatures have differences there of 5 or more (and sometimes as high as 10 different).
There's a lot more ongoing damage, a lot more half damage on a miss, a lot more area effect powers, a lot more conditions, a lot more movement on the board, a lot more extra abilities/damage from magic item powers, more modifiers to saving throws, etc.
Granted, the NPCs have a lot more of this as well.
But, it's not just about to hit percentage.
Note: His AC 44 comment is a bit off. There are 5 AC 44 or higher creatures in the MM. 3 of them are solos. With the PCs having 5 turns per round and the creature (basically) only having one, it is ok for that creature to have high defenses. It will be getting attacked a LOT per round. In fact, out of the 30 odd monsters in the MM with AC 40 or higher, the vast majority of them are Elites or Solos. PCs will not typically be outnumbered or even evenly matched numerically by these types of foes.