4E actually was designed very tightly so GMs could play competitively against the players' PCs in predetermined encounter scenarios. The strength of the ruleset let the GM become a player so they might play as capably as they could using the their game-balanced forces against the PCs in an Encounter. If PCs died, it was part of the game yet still in part due to the GM. The players are more apt to accept character death like this because they know the rules are always in play. They understand they are playing vs. the DM in encounters, but one limited by the rules they are under as well. Not a DM unlimited by rules.
I personally feel this is feature of every edition of D&D. We could argue over how tight the rules were and how well the rules matched the stated intention, but certainly in Gygaxian D&D there is an assumption that the experienced DM provides the players directly (by designing encounters appropriate to their level) or indirectly (by clearly delineating the area of the dungeon appropriate to characters of a particular level) with balanced and survivable encounters, and that there is valid level of antagonism between the DM and the party where within the constraints of what is fair the DM is trying to 'win' and playing the monsters intelligently and creatively. Likewise, there exists 'superior play' on the part of the players that leads to their victory and reward, and character death is an outcome accepted within this framework.
In my own experience, it's quite possible to create very balanced 3.X or 1e encounters once you have some experience with the rules set. Certainly there is as much knowing how to build a challenging but balanced encounter in any edition of the game that seems to me to be an art - 4e is not an exception to this. In my own experience, where this can go haywire is when the players actions lead to encounters you never would have intended. Almost all of the player deaths that have occurred while I was wearing the hat in the last 20 years have been the result of one or more of the following:
a) The party became separated and a small portion of the party ended up in an encounter meant to be challenging for the entire party.
b) While still engaged with one foe, the party pushed forward into a new location, or fled into a previously unexplored area, or interacted with an unexplored feature of the current environment (opening a sarcophagi for example), thereby triggering an encounter with a second group of foes.
c) While in the middle of an encounter, party cohesion broke down and one or more members of the party decided to sacrifice other party members in order to ensure their own survival. Often this involves the strategy, "I don't have to run faster than the monster, I just have to run faster than you." Or one or more members of the party while in the middle of an encounter decide to pursue their own ends rather than assist other members of the party, such as collecting treasure while the fight is still underway.
d) The party gets into an encounter where they lack metagame understanding of the foe (or perhaps false metagame understanding), and becomes confused and paniced, taking wildly inappropriate actions - deliberately switching to weapons which in fact are ineffectual against the monster when their normal weapons are sufficient, not switching to an alternate strategy despite hints their normal attacks are failing to make headway, failing to make an attack at all and in effect perpetually delaying action or otherwise generally taking a wait and see attitude while their allies are in mortal danger, turning non-undead or failing turn undead, choosing to perform spells that offer no immediate benefit, and so forth. Basically, highly suboptimal play as a result of having the resources to win, but not recognizing that they do. This also typically leads to party cohesion breaking down.
I've never DMed 4e, but I imagine that the same sort of general issues can occur if the game is played out in an organic fashion. Door A may have a wyvern, and door B a hydra - neither of which is a threat by itself. However, you may find that the PC's having opened door A, convince themselves that opening door B before dealing with the wyvern is a great idea. At that point, you get PC deaths or else you use some sort of DM force to save them - even if it is only strongly hinting that opening door B is a terrible idea.