I don't get it. Maybe it's the writing. Take this example:
That may seem like an unreachable number, but it’s important to remember that monsters, like characters, aren’t piling on as many attacks on their turn as in 3rd Edition.
Yes, it does seem like an unreachable number, give that monsters aren't piling on as many attacks on thier turn as in 3rd edition. Perhaps the author meant to say that it seems like a 'reachable number'? It's hard to know what the design goal was based on that sentence.
My guess from the rest of the article is that it is to make PC's virtually invulnerable. The goal is to have PC's that can have 'the stuffing beaten out of them without serious consequence'. (Pardon me for thinking that's what hit points themselves did.)
Notice first that the writer is worried that the audience might find these too rules too harsh:
This is less than a 4th Edition character would have, but each monster attack is dealing a smaller fraction of the character’s total hit points, so it should be reasonable. If it feels too small, increase it to one-third full normal hit points and try again.
The writer doesn't even hint that he thinks you are supposed to find these rules too lenient.
Secondly, notice that being at -1 hitpoint is functionally the same as being at -60. No matter how close you are to death, no matter how badly you've been mangled, you are one instant from up and at 'em again. This rather discourages monsters trying to finish a character off. If you've dropped a 200 hit point character to -1, the next 98 damage you do to that character is meaningless. There is also a small chance of dropping unconscious and then gaining hitpoints: "I feel much better now."
I for one have never been disappointed to feed a mortally wounded character a potion of cure
light wounds, and find that they don't immediately leap to thier feet. I always figured that they were for curing
light wounds.
And finally, they hammer the 'NPC's aren't PC's' point again.