Edit: Bad Math.
Well, the simple answer is for balance. Spellcasters are less reliant on magic items by default. Pure physical types have to rely on them much more. A wizard without magic items isn't as disadvantaged as a fighter or a rogue is.
The fluff answer? People are tougher and stronger and faster than they were a thousand years ago, mostly because they can no longer rely on fancy magic to protect them. Does this make sense for the various bonuses? Two out of the three. Natural Armor and even Enhancement (My skin's tougher and I know how to take a hit in the right place to avoid damage)... but less so for deflection.
LOST MY TRAIN OF THOUGHT AHEAD, FEEL FREE TO DISREGARD
Also, magic items are rarer because not only are spellcasters less powerful than they used to be, but there's also a hell of a let less of them. Less in a gross amount but also less proportionally. A thousand years ago, maybe 5% of the population had the capability of casting spells.. that's 500 million. Now, it's probably closer to 1%, which would be 3 million worldwide. If this planet was earth-sized... that would be 1.5 people per square mile, and 1 spellcaster per 100 square miles. Granted, if this were an exact copy of Earth and we took away ocean surface area, Antarctica, and say... 80% of the remaining land area for being inhospitable, that brings us to... about 27 people per square mile and 1 spell casters per 5 square miles. About the population density of present-day Mali overall.
There's a reason this is happening... but it's sort of a plot element.
Granted, there is only so many reasons something like this could happen on a world-wide scale.
TRAIN OF THOUGHT BACK ON TRACK
However! You're right- The increased Point Buy reflects this 'toughening' to an extent.
It could be... that this is whatever power's left putting things back into the hands of heroes. Clerics continue to receive divine gifts and spells (albiet not at full historical potency) even when they can no longer hear their Gods or detect their presence.
[/i] They are no longer being given
divine power but drawing
it from a source. The same could be true of these last effort heroes.
I was strongly considering the pros and cons of this variant and the game without it. If I dropped the variant, I wouldn't be inclined to make magic items any more common. As a result of that, some players might be underpowered in comparison to other members of the party. But then again, I'm always super anal and worrisome about balance and 'lore'.
I don't mind the argument, really.
As for the conversation between Eric and Carl... there's a lot of things neither of them know. "Where do you get your spells? Dunno. Where did the magic go? Dunno. Why aren't we as fertile as we used to be? Dunno. Why do some of us come back from the dead, more often after they've died in the daylight? Dunno. How come some undead who die at night come back with the power to instantly purge other undead? Dunno."
On that last note, everyone occasionally sees blue eyes in a skull when they dream. It's strangely comforting.