In various comments on this site, DW was mentioned as
[Dungeon World/Apocalypse World] is really more required reading for any designer today working on innovation in mechanics
Having read the ruleset, I do not (yet?) see why some posters feel this is such a major step forward.
A few examples of mechanics mentioned as innovations are those:
Moves, unified power mechanics
There is a unified mechanic for 'doing stuff' called 'moves'. Reading the moves, this sounds like 4e powers or 4e monster powers to me. While this unified mechanics is certainly a good thing, it's hardly an innovation of DW. What makes moves special?
Hard boundaries on scaling
There is (almost) no scaling, and hit/miss is not dependent on enemies, but only on attacker. A cornerstone of many rules-light games, and something that can certainly be seen as a good thing. What's different or noteworthy about DW's implementation?
Why is this a good thing? I know it from rules-lite games; when I've experienced this it often lead to a situation where a small part of the group had the majority of the spotlight.
No flanking etc. In-combat positioning and grid-based combat are a cornerstone of dungeon crawls and D&D forever, war game roots and all. How is this supported in DW? Does it even make sense to use a battle mat or grid for DW combat?
XP for misses
Trying to soften the blow on failure is certainly a good goal, but again – nothing unique. It also reminds me a bit of Burning Wheel's "You can only advance through failure" – which I felt was detracting from good game experience.
So… What am I missing?
What are the major innovations in Dungeon World compared to D&D 3.5/Pf/4e? Why is Dungeon World (or Apocalypse World) considered a seminal work for innovative mechanic design?
A good answer would contain a short discussion of each of the major innovations of DW over older D&D variants, and what problem this change solves. This also applies if the mechanic itself is not new but is used in a novel way.