We're not talking about what the characters know. The meta-game information you're talking about is things the characters don't know, though the players might. When you bring up things in the rules and try to use them to invalidate events in the world, that is actually relying on the rule system, something the characters as a rule, do not know.
I disagree. The characters may not know "Sir Fred is a 10th level fighter with 100 hit points, and a fall from a horse can do 2d6 at most", but they DO know just how tough someone with Sir Fred's experience is, and that he has survived far worse falls with no serious effect.
Putting it another way: If someone told you, I dunno, Hulk Hogan, in his prime, was killed when someone through a balled-up sock at him, would you be at least a LITTLE suspicious? To a person who lives in a world which runs by D&D rules, a powerful individual dying from a trivial damage source is just as odd.
Sorry, but this particular example isn't a good representation of the problem, which may come up with regards to meta-gaming such as has been the issue here. Eladrin being able to teleport isn't something that would require rules knowledge to know.
I've got to go now, so I can't give a better example at the moment, but that's why I don't consider yours to be a problem. It's not a rules issue.
It's an example of the larger problem dicussed here, that of shaping the world so that it makes sense according to the rules. While there's always been magic, etc, in D&D, 4e introduces a common race, found in multiracial cities, which can teleport once every 5 minutes to someplace in LOS. This instantly changes how jails must be designed, and the nature of how the law will be enforced. Another good example is wizards. Pre-4e, you could bind and gag a wizard, or even just take away his bag of components, and you could be FAIRLY sure he was harmless, feats like Still Spell notwithstanding. But in 4e, a bound, gagged, wizard can blast Scorching Bursts all around him. He might not be able to aim them, but he can cause a lot of havoc. So, again, the world has to reflect this. If it doesn't, the world suddenly becomes a lot less believable.
Likewise, if the way healing works when the PCs aren't looking is different from how it works when they are, it makes the world make less sense. I have no problem with someone saying that "PCs (and their allies) simply don't take serious wounds in combat, unless you actually die", but then I'd like it stated that the use of healing surge powers, whether martial, arcane, or divine, don't impact the "seriously wounded", however defined. To some extent, NPC vulnerability is handled by the fact they usually can't activate their own surges, but this still doesn't allow an NPC to be injured without being able to "sleep it off", except by simply handwaving it. A world with no injuries other than "annoying" and "fatal" makes no sense, and I don't like having to rule that if a PC wants to heal an NPC, they can't, because of all the questions that would raise.
These things stick in the back of my mind and keep me from enjoying 4e as much as I should.