Elo hell exists but only from a player's perspective. It does not exist statistically. A player that does not belong in an Elo range will always move out of it after a large number of games unless there is a crutch keeping them there (Kassadin in Dom, Darius in TT, premade carrying in 5's, duo w/ smurf in solo, etc.). In Elo hell, from the player's perspective, the losses are infuriating while the wins are unsatisfying. But statistically, if that player doesn't belong in the range then he will be a constant strength in his games, making his team randomly have up to 4 leavers/feeders while the enemy team can have up to 5 leavers/feeders.
The difference between a high Elo player and a low Elo player is not skill, otherwise Nekrogen would be negative Elo (hueheuhue like he's going to see this post). The difference between the two is the willingness to look at mistakes that you made and learn from them. These mistakes can be in both micro/builds and in teamwork/strategy -- for example you're a ranged ADC running up to a post-windmill 3v4 fight that your teammates started and are losing, and you could either jump in and finish off two very low people before dying and leaving one enemy survivor to cap the point, or you could abandon your teammates and defend the windmill against 1 healthy enemy and 2 heavily wounded ones that will likely recall. Your teammates might not understand the latter is better, but your teammates were out of position to begin with.
The difference between a high Elo player and a mid Elo player is mostly counterbuilding and counterjungling, or rather roaming with accurate expectation of enemy movement in the jungle. It is impossible to know where the enemy is perfectly, especially if he's been missing since he died. Very often I will not push bot lane because I simply don't know where the enemy assassin is -- and then I see them top and that I should have been pushing the last 15 seconds. Were they headed bot and then figured I was backing and changed directions? Or were they headed top from the start? Dunno! There is still quite a bit of good guesswork going on, especially when you know they actually are in the jungle and you're also hanging around in the fog.
If you can get replays of games you were in and then watch them with only the enemy's vision turned on, it helps a lot.