What's the difference? The game world is being changed as a result of a failed skill check. Had the check succeeded, the rope would have never broken and might never break. So, it's not a weak rope. The cliff face suddenly crumbling because of my climb check? How is that not my skill check (which is ONLY my ability to climb something) causing a physical change in the game world. After all, the next person might climb the same cliff and nothing crumbles at all.
The only difference is that you find one physical change to the game world more palatable than the other. But, in both cases it's a change to the game world being introduced without any connection to anything. Sure, flying pixies are extreme, but, again, it's only a difference of scale, not kind.
How is one skill check changing the physical properties of the game world acceptable, but another one isn't? Other than your personal preference of course. ((And note, I'm being pretty hyperbolic here- I doubt any DM would actually introduce pixies, but, I'm trying to show a point here))