I said Dark Sun, despite not having played it, because from what I do know it seems like it'd work well to highlight the "grim and gritty" aspects of 5e. (But of course Dark Sun has psionics and bug-men so maybe it wasn't the awesomest choice.) But ANYWAY.
This edition, probably more than most editions, seems like it will have an implied setting. Warlock pacts, sorcerous origins, and arcane traditions ALL look like they'll come with a lot of implied story. And last I heard, each god will get its own cleric domain, rather than a list of options like in 3e - and since they pretty much need to include a list of gods for new players, this means that those gods will be fairly intimately tied into the "default" playstyle.
And that's not even getting into the classes we haven't seen yet - which, from everything we've heard, will be even MORE specific than the core classes. I expect paladins and monks to be associating with specific orders that have specific rules, charters, and benefits. I would even expect barbarians to choose from particular tribes.
Personally I dig this a lot. Don't just give me a wishy-washy pact that says "star-pact warlocks make pacts with creepy star-related things." Tell me exactly how and why Shub-Niggurath is subverting my lust for knowledge to turn my mind inside out, or whatever. Ambitious home-brewers and roleplayers will come up with their own stuff regardless, likely inspired by the cool fluff WOTC adds. But it does mean that the "default setting" will probably mean more in 5e than it did in, say, 3e, where you could pretty much only tell it was Greyhawk if you were reading the religion section.