Another sort of problem: Marvel Super-Heroes. Since characters are essentially static, is it possible to meaningfully categorize those encounters as status quo or tailored?
This is an issue of genre. In the classic super-heroes genre, the heroes are a force for the status quo. They are reactive to the super-villain of the month and his mad scheme to change the status quo in some way. A super-heroes campaign modeled on the classic Silver Age Marel or DC universe would necessarily involve the GM manufacturing diabolical plots and inflicting them on the campaign world as being the primary off-ramp to each session.
(And note: This isn't a bad thing at all. Rather, it'd be pretty well expected by any of us who started playing in a super-hero campaign.)
A sand-box-y superheroes campaign would have to involve a pro-active hero wanting to change the status quo. Think of the Punisher or more modern versions of Batman, where the city is portrayed as a cesspool and our hero is cleaning up the town one mob boss at a time. That could run in a fairly hands off-way by the GM, allowing the pc to explore the seedy underword and react towards what he finds accordingly.
This brings us to the heart of the epic fantasy problem for sand-box play: the stereotypical epic-quest hero is an unlikely/reluctant one. The general assumption is that there is some evil dark lord who would take over the world but for the exploits of the orphan farmboy. This isn't to say that epic quests can't involve pro-active, motivated central characters, but that those epic quests will look more like the Quest for the Holy Grail than they will Lord of the Rings, and necessarily be more episodic and picaresque.
Put the unlikely/reluctant hero in the sandbox, and he's going to just stay a farmer. Put the swords & sorcery hero into the sandbox, and he's going to attack it. The stereotypical swords & sorcery hero wants to shake up the stats quo - usually the the empty status of his or her money bag - and proactively works towards doing so. Generally, when the swords & sorcery hero makes a move against a "dark lord" type character it's because his direct interests clash with that of the "dark lord's," not because he must do so to save the world.
This also shows why O(A)D&D pcs were largely assumed to retire a bit past "name" level... Once you've won your kingdom, once you're able to lay waste to swarms of enemies, once you've become "the power," you will generally become a force for the status quo. In this case, the new status quo that the pcs have created. The lower level characters (henchmen, replacements for dead pcs, secondary pcs, etc.) can continue to be the rabble-rousers unless and until some major world changing force comes along to threaten the higher level pcs' blissful retirement.
To sum up... a sandbox campaign is probably going to look more like a Spaghetti Western than a Silver Age comic book. (I remain convinced that Keep on the Borderlands was inspired by A Fistful of Dollars.)