I have to disagree. Half the monsters in every 3e MM being below level 5 was a huge problem if you ever wanted to play at level 8+. Especially when you hit level 13+, there were only maybe 5-8 monsters of each level, and 3e was a system where you had 10-13 encounter per level.
In 4e, you can easily hit level 25+ and have a new monster in every combat encounter. That's more how I like my Monster Manuals to be.
I see your point, but by the time my players reached 8th or 9th level, I would have the MM II or a 3rd-party monster book. I would have preferred the MM I to focus on the hieroic tier, MM II on the paragon tier, and MM III on the epic tier, with each MM having some monsters for the other tier.