I thought the question was "how did you get away with narrating serious injury in 3E, when every non-fatal wound will heal naturally in a week or so?"
A response about natural healing can't be "it's magic!", by definition.
How are you defining a serious injury? And why is the assumption that I must be narrating every hit as a serious wound? I don't understand how that misconception gets created.
Furthermore, you are assuming 3rd Edition rules as my preference, which is not the case. It is the one I've played the most, but not my preferred edition. Now, using the standard 3E rules, a 3rd level character with 30 HP dropped to 0 will take 10 days to recover, or 5 if he does nothing other than sleep in a bed for all 5 days. In 4th Edition, that same character will heal in 8 hours.
Now, let's consider 2E (the edition I do actually prefer), 1 HP per day, or for full bed rest 3 per day + Con bonus per week. Even if you assume the fighter (warrior) has an 18 Con, that's still only 25 hit points of natural healing in 7 days. So it's 9 days of complete and total bed rest. And that's 216 hours. (Not to mention specific only to the fighter. It's longer for every other class) Versus 4E's grand total of ... 8 hrs.
Yes, the 5 days (or 9) of complete bed rest is unrealistic, but not nearly as stupidly fast as 8 hours. It's the difference between 8 hours and 120 (or 216) hours. That's 15 to 27 times longer. And that's if we're not considering characters that are still actively moving and fighting and taking more damage along the line.
It's a matter of attrition over time, and 4E doesn't allow for that, and neither do the playtest DDN rules. In all previous editions, the wounds/HP loss carried over from day to day. In 4E and DDN, you either die in one day, or you heal back to full as if you were never hit in the first place. That's a major problem with how I game.
And, thankfully, DDN is supposedly being designed such that it can support the style of play that I desire as well as supporting the style of play that 4E fans like.
Edited to add: And in a world with magical healing, sometimes I could get away with narrating a more serious wound, with the assumption that characters WOULD spend resources for magical healing, and thus would not rely solely on natural healing.