I figured I'd dredge up some old wounds, because the tonal change to the game that the OP spoke of is something I've been thinking about for several years now. And I'm bored. So, I'm going to say a few words on the nature of safety nets across the D&D editions.
These safety nets are the things that have been added to the game to protect one's character from dying. And over the years, they have become many. Yeah, there are the obvious ones - the classes having larger hit point dice, higher attributes with better bonuses, better ACs. And all of those things do help protect characters from dying. But they are just the smaller nudges. They are a part of the whole, but the big nudges are often much less direct.
For instance. No more Save vs Poison or die. Now, it is Save vs Poison or lose a few Attribute points, temporarily. There are still death poisons, but they have been made rare. Which has a number of effects. For one, creatures which used to be remarkably deadly are suddenly pretty weak, and that makes dungeons a less deadly place to be, since one knows one isn't going to suddenly face creatures that cause save or die rolls. And really, save or die rolls are pretty much out in general, making dungeons a much safer place to be overall.
Many traps remain the same, damage-wise. But character hit points have increased. A 3d6 fall just isn't what it used to be. And many characters have means of reducing or even eliminating damage taken from certain types of traps, on top of it. Which means traps are now a much less serious threat than they once were.
Spellcasters have an increased number of spells per day, and they have many more healing and protection spells available to them. The healing line is no longer Cure Light and a long wait over many levels for the next healing spell. Instead, there is a new healing spell introduced every spell level, each one better than the last. Coupled with the increased number of spells per day and the fact that the good aligned can turn any spell to a healing spell means that healers can now do a great deal more to protect the party from dying than they used to. And that's even before healing surges get involved. No more need to wait for a healer to get to you. You can protect yourself from dying.
And then there's disabled and dying instead of just dead. These days, no one dies until they reach negative CON. Where before, in Basic, you were just dead. That's a bunch of free extra hit points that everyone gets, effectively doubling or even tripling a 1st level character's hit points. Which not only pads a character's life expectancy, it gives everyone a fairly decent span of time in which they can "save" a dying character, instead of simply having the character be dead. Couple that with most GMs not aggressively having enemies go for the kill against all dying characters, and a party can readily be restored back up to full strength as long as a single character survives the fight. Which makes fights that much less deadly.
And then even if you do die. Being brought back from the dead no longer causes irremovable injury, even the lower level version. All penalties can be wiped away. There also is no longer the risk of permanent death with a resurrection survival chance roll when being brought back. Which together puts bringing someone back from the dead much more readily into people's grasp. One top of that, there is more treasure available, and selling and crafting magic items has become an official part of the rules. Which means affording to bring someone back no longer is the economic burden that it once was. Meaning, even those who "die" don't necessarily stay dead for long.
But, it's not any one of these safety nets that makes the difference. It's all of them together. And it's not just the protections themselves that change the nature of the game, it's the fact that together they set a tone. Players look at all of those safety nets, and - even if only subconsciously - they form the opinion that their characters are to be protected from death. That, to the point where people will say things like: "A good GM only ever kills a PC for story reasons". Or "A good GM wouldn't let the death by poisoning stand. He would have the poisoned character fall comatose, and then give the Players a week to find a cure." Which are, essentially, recommendations that GMs interfere with the game with deus ex machina in order to protect characters from death. Which is a whole nother set of safety nets.
Now, a particular GM can, of course, change all of these rules. But most GMs do not readily make that many fundamental changes to the rules. Instead, they nudge rules here and there, if they make any changes at all. Because otherwise, "they're not really playing D&D".
When was the last time you had a character die? Not dying. Dead. Where you wrote "killed by X on date X", folded the paper in half, and set him in your character cemetery. People don't even have character cemeteries anymore. They don't need them, since they no longer have dozens of dead characters. My Basic, AD&D, 2nd cemetery had 132 fallen in it. Mostly from Basic. My 3rd, Pathfinder, and 4th total dead so far across several GMs is 1. And that 1 was for story purposes.
With much less risk of death, there is much less penalty for taking risky, heroic actions. Which fits in with the overall tonal change that occurred across the editions, which many have remarked on, shifting away from a gritty adventure to a heroic epic.
