I overlooked one component of the shift toward "invincible" PCs in the game. The impact of video games on the hobby.
In most video games, there are save points, reloads, respawns, or some other mechanics to allow you to return to where you left off, or close to it, in the event that your character dies. To me, the need to import this mechanic into a table top rpg is based on flawed thinking.
In a video game, at least early on, and somewhat still in single player console games, the whole venture is a solo quest. While you may have a party of a handful of characters, there is generally only one player. If the game never lets you die, it quickly becomes boring. On the other hand, if you have to start over every time, the game becomes tedious to the point of frustration and quitting, considering that some modern games have hundreds of hours of play time.
Even in newer, multiplayer games, such as the World of Warcraft mmorpg, having to start over at level 1 every time your "guy" dies would ruin the fun, since you're part of a guild of players who will continue on if they didn't die. The game simply can't adapt to having a low level character running around with a bunch of high level characters without killing the new guy every time a monster shows up.
D&D and table top rpgs in general have a unique feature that all video games lack. A DM. The DM can tweak things to fit a replacement character back into the action. Or variant rules such as Hackmaster RPG's mentor/protege system can be used to make the replacement character something more than a 1st level whelp. An existing henchman or NPC ally can be promoted to full PC'hood. etc. The flexibility of the rules means that one, or even all of the characters dying does not mean that the entire story has to end and reboot from the start.
Even when we suffered a TPK delving the Caves of Chaos, the overall story continued. We found the bodies of our doomed predecessors. We heard tales of their fate from bards and travelers, etc. The story moved along, and we stepped back into it.