He's talking about player defenses there, which is a seperate issue.
The problem is every character needs an additional +1 per tier to match the scaling monster defenses at certain points in that tier.
Actually, that's a separate issue. I'm not so worried about your non AC defenses not increasing when light armor increases due to masterwork, mostly because there are paragon tier feats which add to them.
No, the issue I was pointing out is that at 4, 8, 14, 18, 24, 28 you increase only 2 stats, affecting at maximum only two non AC defenses. For example, my barbarian is a 18 str and 18 con warforged. His fort defense is 4 higher than his will, and his reflex is 1 lower than the will. And this gap will widen as he levels due to never putting a point into dex or wis at the 4, 8, etc levels.
OK, so 3 issues with DnD math as you level.
1. Attack bonus falls behind, compared to the rate monster defenses increase, at about 1 point per mid tier.
2. Maximum non AC defenses fall behind by 1 point at paragon, 2 at Epic, but there are feats to increase these at paragon.
3. Minimum non AC defenses (everyone has at least one) fall behind at 8, 14, 28, due to lack of increases to all stats at these levels.
Solutions?
1. Add 1 to hit at 5, 15, 25 or something.
2. Do nothing, or perhaps add 1 to them at 15, 25.
3. Increase all stats instead of just two at 4, 8, 14, etc.
Implementation? WotC: Supergood Feats! (sweep those last two under the table)