As usual, you may be right. At least, this may be how the game has been written to be played.My view is that 4E is "high-concept" simulationism. "You play a Hero in a land filled with darkness and monsters; as a Hero, how will you react?" (Specifically, a priority placed on System + Situation.)
I think the 4e rulebooks - like other D&D books before them - tend to underspecify the distribution of authority between players and GM over issues like PC backstory, world creation, etc. There are things that push both ways - the PC sketches in the race descriptions in PHB1, for example, tend to suggest that players have a lot of freedom to describe the gameworld and their PC's place in it, whereas the DMG and especially the published adventures tend to assume that the GM has the authority to set "plot hooks" that are more-or-less independent of the PCs and the players.
I think the former tendency is what enables the game to be read in a narrativist light, while the latter suggests high concept simulationism.
In books like The Plane Above or Underdark the conflicting tendencies can be identified being parcelled out between sections of the work. The descriptions of the mythology and the gods' realms tends to suggest backstory that the players can choose to engage with as they see fit - do they travel into deep myth to stop Bane killing Tuern, for example, thereby putting an end to some earthly dictatorship, even at the risk of this letting the Primordials win the Dawn War? Wheras the descriptions of the Outer Isles in The Plane Above, or of many of the locations in Underdark or The Plane Below, seem designed to support the sort of exploration of situation that you describe.
As far as exploration of system is concerned - given the nature of the system, I think that gamist play is an ever-present emergent possibility once exploration of the system becomes a serious priority. Both character build and combat - the two systems rich enough to support serious exploration - clearly admit of winning and losing moves.
I think that focusing too much on exploration of the system is likely to lead to the sort of divorce you talk about between fiction and play - which takes me to your next points!
My own view on the "realism / verisimilitude / believability" issue in 4E is that it's not really about any of those things. To use Forge terms, it's about Exploration; 4E is light on Colour. All that means (assuming I'm using the jargon correctly) is that the details of the imagined content doesn't have much of an effect on how the game plays out.
I think there are two issues here. First, what parts of the fiction are brought into play? As I've posted before, I think that the 4e combat rules cannot but bring the fictional geography into play. In a game in which fantastic combat is a good chunk of play, that can be a good thing.We've all played us some 4E and we're familiar with the mechanics. We can see how the way the fictional situation isn't as important as it is in Sorcerer
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Let's say that two characters are flanking a gelatinous cube. Another character, perpendicular to these two, fires a scorching ray at the cube. I describe the cube as lurching to one side, stretching out, one thin strand connecting two bulky masses.
Now most of its mass is on one side and it's revealed a weak point. What happens if I say that I'm going to cut that thin strand with my sword? If I'm a Rogue, do I get Sneak Attack bonuses to my damage? If I want to trip it, does that make it easier? Can I flank it now?
It's the same thing with 4E or my experience with Freemarket - the rules say that an ooze can't be flanked or sneak attacked or critically hit. So it can't.
If the same situation occurred in Sorcerer, the DM might award me some bonus dice for excellent tactics (if I cut at the thin strand). Thus reflecting the fictional situation, emphasizing it, no house ruling required.
But the second issue - which I think comes closer to what you are concerned with - is the way in which skill checks, skill challenges and improvised actions more generally are adjudicated. In the gelatinous cube example you give, it should be open to a player to make a Dungeoneering check (or Nature check - what skill covers monster knowledge for oozes?) in order to get bonus damage or a bonus to hit, in much the same way that p 42 of the DMG suggests that it is open to a player, upon hearing the description of a hanging chandelier, to make an Acrobatics check to get bonus damage or a bonus to hit.
I think that the game has, in principle, the resources to handle this, but doesn't deploy them clearly. I see two problems, and I'm sure there are others. The first is the reluctance to elaborate on the interaction between skill checks/challenges and combat, which is reinforced by the frequent description of skill challenges as "non-combat encounters". The second is, even within the framework of skill challenges, the failure to clearly set out the way in which the fiction is to unfold as the challenge progresses, with the unfolding fiction itself determining the range of options and difficulties for subsequent checks within the challenge. I know from experience that, when you run a skill challenge in this way, the players will pay attention to, and tailor their responses to, the fiction.