Whether it ultimately survives the playtest or not, WOTC has put a lot of thought into this mechanic. Lets take a look at some of the simple beauty:
1) Its modular. Because it is not tied to magical healing or combat healing, DMs can modify it without having too large an impact on the game.
Don't like the mechanic, then drop it. You need your clerics or buckets of healing potion, but the game moves on no problem.
Not enough, bump it up. Combat healing remains the same, but your party can take on more encounters without running out of juice.
2) Provides randomness without being too random. People love to roll, but overall hitpoints are too important to leave to chance. However, recovery is more granular, and particular good/bad rolls don't have the same measured impact.
On the other hand, players can use average values to regain the consistency of healing surges should they choose to.
3) Better flavor. I never minded surges myself, but I understand the concern with those that do. By separating this mechanic from in combat healing we can separate the mundane and magical flavor.
A person can now recover from their wounds in part by resting, but in the short rest way that dnd adventurers typically assume. However, this mundane healing has its limitations (and seems to provide 1.5 - 2x the pcs normal longevity, as opposed to 3-4x for a 4e character).
Overall it seems like a good compromise to me, but again the key is by making the mechanic modular enough, DMs do it with as they please. While they could do the same with healing surges, it affected a lot more.
One thing I am confused about though. The article went into a lot of detail about how 1/2 HP means true wounds and the like, but I didn't see any mechanics to support that. For example, this Hit Dice healing doesn't seem impacted by whether I'm healing at 90% full or 10%.