As a game developer myself, I can see the "percieved" mathamatical problem that the CharOp people are talking about.
Is there an inherrent discrepency between PC Attacks/Defenses, and monster Defenses/Attacks.
Yes.
Is this a problem?
No.
Why?
Because of the following reasons.
1) In the Heroic Tier, your characters are the equivalent of raw recruits. Sure, they have a few tricks up their sleeves which have likely made them cocky and over-confident, but they don't have much "real world" combat experience.
As such, a game system which is more forgiving of the "mistakes" that the party is like to make at this level, both as a result of a lack of teamwork synergy, and as a result of player experience.
You must remember, the Heroic tier also represents the Training ground for players themselves... Not only is the heroic tier the place in which 4E Noobs will be learning the rules of the game, and the basics of tactical and strategic thinking.
Furthermore, it is in the Heroic Tier where player's (both new new and experienced players alike) learn to get a feel for their character's strengths, weaknesses, and start to develop a play-style for that character.
It is also at this level, where the player's will start getting a feel for the strengths, weaknesses, and play-style of their fellow characters and (hopefully) start developing complimentary tactics.
At the very least, this tier gives player's an opportunity to figure out the basics of their character's own abilities and at least learn where they are most beneficial on the battle map, given the party's composition and individual play styles.
All of the above factors have little (if nothing) to do with the inherrent "math" of the game!!! - Yet all of them play an important part in how any given encounter will play out.
Is it any surprising then, that given how many uncontrollable variables exist at this level of game play, that the game's inherrent math is more lenient?
For those who like to compare DnD to an MMORP or a video game - the heroic tier is like playing on "easy" or "normal" mode.
By the Paragon Tier the party is much more comfortable with each other, and should be starting to form well established combat routines, both individually and collectively as a whole.
After playing through the heroic tier together, each player should not only understand their character's abilities and role within the party, but should also have developed a good understanding of their fellow player's unique play styles, and how they influence the way in which they play their character(s).
Furthermore, each player should know where their character is best positioned on the battle grid, which of their party members they directly support (or are supported by), and which monsters are their ideal targets (Lurker, Soldier, Leader, Brute, Artillery, etc).
Again, while all of these factors are influenced by the mathematical abilities of any given character, they are far more dependant on other, less transparent factors.
However, given the fact that the player's should now have developed a solid understanding of their teams inherrent strengths, weaknesses, and strategies - the game becomes slightly more challenging, and the "math" skews slightly against the party - forcing them to learn how best to gain (and take advantage) of situational modifiers while still being forgiving of their learning curve.
It is also at this level where DMs will start shaking up encounters, forcing players to adjust their "favorite" strategies to deal with less-than-ideal situations, or against less-than-ideal monster roles.
Going back to the video game analogy, this is like playing Dnd on "hard" mode.
By the Epic Level, the 100+ hours spent together at the game table with the same characters should have forged the party into a Navy Seal unit - with each player at the table having intimate knowledge, not only of their own characters strengths and weaknesses, but of the entire party!
It is at this level when the "kid gloves" come off, and all that experience is put to the test.
Completing our Video Game analogy, this is like playing DnD on "Nightmare" or "Hardcore" mode.
Is it any wonder that the odds are stacked against you?
