Presentation plays a large part on how something may be viewed.
Well, as @Oofta pointed out, SCs are pretty rigid in their default format. So you can see this as a bad thing, or you can see it as a good thing. In Story Now play, it tends IMHO to be a good thing. This is because when the PCs in the above scenario are faced with a challenge, the MECHANICS of that are already handled by the rules. It isn't up to the GM how many checks are needed, the DCs, etc. I mean, the GM can choose a bigger or smaller encounter budget (complexity), but that's it! They can pick the primary and secondary skills, but they have to pick some and there's a tightly constrained number of them. Really all the GM is doing here is binding the SC framework to the specific fiction! So, basically, any judgment calls during play notwithstanding, the GAME set up the scenario and determined how tough it would be. The fiction is not ENTIRELY color, because it can do things like disallow some approaches entirely, or suggest alternative ones, but play is very principled by this structure. You can think of the entire level of play (1st level) the same way, there's an XP progression, XP budgets that establish rewards, treasure parcels are spelled out, etc. Nothing is really up to the GM in terms of how that structure works. @Manbearcat can parcel things up, so have different numbers of encounters and SCs and Quests of certain levels that add up to enough XP to advance a level, and can dole out short and long rests, and to some extent milestones. This is far from nothing, but the players are at least guaranteed a certain minimum standard of how things will go that is purely built into the game.
Right, I was just pointing out that a DW danger can be a lot more threatening to one PC than another, so its not like you can't get into a bunch of detail about what the threat is, how does my PC match up against it, etc. I mean, the other obvious example would be combat! A wizard is not going to fare well in a melee with a goblin! The fighter OTOH will probably chuckle has he cuts it in pieces. Frankly I've never missed the whole 'numbers thing' when playing DW, its remarkable how little it actually added to the game! I mean, DW doesn't even have melee rounds, yet combat works fine...
I think the point was to point out that this is NOT true in a game like Dungeon World. The rules are quite prescriptive and quite descriptive as well. The description and prescription just don't happen in terms of time units, feet, etc. Instead its "scary deep chasm that might be too wide for me to jump" and that's just as good!
So if I have it right, the introduction of the chasm is not the issue, but rather that the DCs and the number of skill checks required are not prescribed through the game mechanics but rather the DM, and to that end the DM is the final arbiter of what skill is rolled for? Hence @pemerton's suggestive comment.
It definitely can, maps are a part of DW, they are just 'incomplete' (so that the participants can inject new fiction somewhere). The GM might annotate a map with "hard to jump across chasm" or something to call it out as a danger.
I think it is assumed that dangers will show up in all this ilk of games and that GMs introduce them. So, no issue with the chasm being introduced, no. In 5e the DCs are entirely up to the GM, yes. I presume they also decide what skill will be used, though I'm perfectly willing to cede that one, as its unlikely the players will let the GM get away with Streetwise...
I think in a more general sense of overcoming obstacles the GM in 5e is entirely free to determine how many checks are required, and what kinds, but again may be constrained by a need to not be a dick about it. So probably the GM is stuck with 'Chasm: 20' wide' and thus jump/athletics, a single check, etc. 
Agreed.
Two points. One, I do think that could actually work, but it would require rather a lot of preamble: the chasm isn't just some random place in the wilderness, it is a settled, populated area, and people cross the chasm on various bridges, ropes, jumps, etc. In that circumstance, I could see Streetwise being used for "cross a chasm" when one wishes to do so unobtrusively. But for the usual expectation of "cross a chasm," that is, in the middle of nowhere with no one but the denizens of nature nearby, sure, I could see a problem there.I presume they also decide what skill will be used, though I'm perfectly willing to cede that one, as its unlikely the players will let the GM get away with Streetwise...
Theoretical absolute latitude, which carries such heavy costs no one is willing to use it, vs practical quite constrained latitude, which only allows that which won't ruffle feathers. Hence why some (I think including you?) have noted the advantage of having actual rules one abides by: you're giving up the theoretical absolute latitude in order to gain practical latitude that is much less constrained. In other words, the actual meaning of "social contract" theory, which doesn't really work for IRL politics (since no one consents to the country of their birth, and thus cannot consent to the initial social contract) but works quite well here. GMs agree to give up certain freedoms that they were unlikely to exercise anyway (like the freedom to say "rocks fall, everyone dies" for no reason) in order to secure the rights to doing rather a lot of things that might have set off alarm bells in the "state of nature."
I think this is where the theoretical-absolute vs practical latitude distinction is useful. In theory, the 5e D&D DM has no constraints at all, aka "the rules are merely suggestions." In theory, the DW GM has several constraints, some qualitative ("be a fan of the characters") and others quantitative (you must answer Discern Realities questions honestly.) But, in practice, the 5e DM cannot realistically use the vast majority of their theoretical latitude, because it would upset the players and/or damage the group's game to do so. Contrariwise, the DW GM not only can but is expected to use every ounce of the latitude they are given, to push the envelope ("think dangerous," "think offscreen, too"), drive the action forward ("make a move that follows," "ask questions and use the answers"), and enliven the experience as much as possible ("embrace the fantastic," "give every monster life.")
The problem with many such things is, without specific detail, the example will be (perhaps rightly) criticized for not being something anyone could actually encounter, or too general to give any information; but with specific detail, the example will be (perhaps rightly) criticized for individual details that are not salient to the discussion, or too specific to permit reasoning from it.
