AbdulAlhazred
Legend
Moot point.
As a DM, I can say that the corner of the wall you just moved behind for "cover" is crumbled in despite the bold lines I drew on the grid and doesn't provide the bonus you expected.
As the DM, it's your duty to describe the world and fill in those details on the fly. As a player, it's your job to ask questions that help the DM fill in those gaps. "Would that corner provide me cover?" "Only slightly, it's not a full wall, but a crumbling ruin of one..."
Therefore, the real problem here is not "rigid battlemat play" versus "loose DM rulings". The real problem is description vs. real world cues (battlemats, minis, etc...); and it's something 4E fails completely at.
If Mearls wants to design the perfect 5E, that uses real world cues to segue into the shared fiction, he's going to need to design rules that allow and inspire that.
Part of that is giving DMs guidelines to make rulings based on what is going on in the fiction and the real world.
This is the challenge 4E faces currently, as the combat rules (which use the real world cues the most) poorly translate into a vivid fictional situation that the "loose" rulings favor.
So, the question Mike needs to be asking himself is, "How can I utilize those real world cues to efficiently and effectively translate a vivid fictional situation?"
I think this is false though. 4e never anywhere even hints at any resistance to the DM applying any kind of adjustments to the rules or alternate rulings in any situation where it is warranted. All it does is give you a solid basis for easily handling the 99% of walls that aren't crumbling. The crumbling wall doesn't give cover. Heck there's a default mechanic for that too, it isn't blocking terrain. You can add additional considerations as you like. Maybe the wall collapses if it is hit by an attack. The structured combat rules aren't designed at all to rule out things, they are simply designed to deal with the trivia in a simple fashion and leave you with the creative and interesting stuff. 'Real world cues' are for the DM to devise, no rule system can tell you what to do there. I mean did 1e tell you how to handle a crumbling wall? I don't recall that it did, but we were able to, except we also had to handle all the other walls and corners on our own as well...