[MENTION=6693711]slobster[/MENTION]
See, mine will. They know how things work, they own a lot of monster books. If I simply took a monster and gave it the numbers it was "supposed to have" absent the underpinnings of level and ability scores, they'd know, and I don't think they'd be too happy about it. I wouldn't, in their shoes.
When I read this, something clicked with me.
3rd edition started to do the same thing 4e did towards the end, it just did less openly.
Later 3e monster books started tailoring the math too. For example, undead started getting "Unholy Toughness" which gave them more HP than they were entitled to by the rules.
Other monsters got a somewhat forced power attack in their specs to represent more damage and lower attack bonuses.
And natural armor has always been a way to get a monster's AC into the appropriate range.
So if created a monster that had a +11 attack bonus, when it "should" have a +15, then I can just say its got a "clumsy" trait that gives it a -4.
And that's the bottom line. 3e tried to make everything explicit, every tweak had to have a justification. 4e said, here are your numbers that will give you a good encounter. Feel free to adjust the justification for those numbers to your liking.