Isn't the whole point of the rules that you can't get *all* your defences good?
I mean why bother with different classes, with different defence specializations, and mosters that attack different stats if your just gonna perma buff the NADS (which do scale with level anyway).
The problem is that the NADS don't scale *enough* in relation to monster attack bonuses. This is only a problem at higher levels of play. The differences at character creation are just fine.
The math has been crunched elsewhere in more detail, but as a quick example, let's take two characters, a fighter and a fey warlock, and compare their fortitude - based on a 18 str for the fighter and a 12 con for the feylock.
Level 1:
Fighter - Fort 16
Warlock - Fort 11
A level 1 creature attacks with a 4 vs Fortitude, and hits the fighter on 12+, the warlock on 7+. Not unreasonable.
The fighter boosts his strength every time, along with wisdom or dex. The feylock boosts charisma every time, along with int. At level 11, all stats go up by 1. The fighter now has a str of 21, while the feylock has a con of 13. Lets say that having just reached paragon, they still have +2 neck items.
Level 11:
Fighter - Fort 24
Warlock - Fort 18
A level 11 creature will have increased its attack value by 10 during this interval (1/level), for a 14 vs Fort. It hits the fighter on a 10+ and the warlock on a 4+. Even with an instant upgrade to a +3 neck item, the monsters still hit more easily at this level than they did at 1st.
On the way to epic tier, the fighter continues to boost str every time and is up to 24. Let's say the warlock boosts int and con, for a total of 15 con. With +4 neck items at level 21 it looks like this:
Level 21:
Fighter - Fort 33
Warlock - Fort 26
The difference between them is up to 7 (starting at 5 at 1st level). The level 21 creature attacking with 24 vs. Fort will hit the fighter on a 9+ and the warlock on a 2+. Even with a +5 neck item, this is still not scaling evenly. There are items and feats to help make up for the monsters' increasing to hit bonuses, but let's focus on the difference between the characters for now.
So on to level 30, boosting the same stats as last time; fighter takes strength up again, while the warlock boosts con once and int once (along with charisma). This gives the fighter a 26 strength, and the warlock a 16 con. Assume +6 neck items, and no feats or NAD boosting items.
Level 30:
Fighter - Fort 41
Warlock - Fort 34
A level 30 creature attacks with 33 vs. Fort, hitting the fighter on 8+ and the warlock on a 2+. Even trying to boost con a couple times, and starting with a 12 CON didn't stop the warlock from being hit on a 2 in epic tier. By raising con, she managed to not drop further away from the fighter - but a character that didn't boost their Fort stat twice would have fallen to a difference of 8 at level 30 (vs 5 at level 1).
This is why there are many house rules regarding NADs and how to boost them. I ban the expertise feats and Paragon defenses, and instead grant all characters Math Expertise for free. It boosts attack rolls and NADs by 1 at levels 5, 15, and 25. Furthermore I also allow 3 stats to be raised at the 4/8 levels (4/8/14/18/24/28). This helps alleviate the discrepancies, and allows for some choice among the characters. They don't *have* to boost their weak NAD stat, but it makes it easier for them to do so.
No one is trying to make the warlock have the same Fort as the fighter; they just want it to scale more evenly, so that difference stays closer to what it started as, rather than getting worse and worse in relation.