Uh, this has been going on a lot longer than recently. I mean giant monster movies where cities got casually wrecked used to be hugely popular, under the thin justification of "it's a metaphor for nuclear war"... when really it was the fun of watching the "rampage" of two super cheezy monsters (dudes in rubber suits) having an equally ridiculous battle and causing stupid amounts of collateral damage while it goes on.
In super hero comics, stuff getting wrecked to crazy extremes ALWAYS happened. The 1960s (when Yahtzee talks about people being nice and content) is actually when a lot of the most popular comics from Marvel really hit their stride. Marvel are the guys who addressed the whole "wow, how does anything survive after all of this fighting" question by inventing an organization called "Damage Control Inc." which is under contract to pretty much run around and fix everything after huge scale battles and events. They even showed up in-comic a few times, and had their own (very limited) series.
Not to mention games like say "Rampage" where you take on the role of a giant movie monster and proceed to run around demolishing buildings for points, and devouring humans for health.
If you want to get technical, I think the reason why your seeing this kind of thing is movies is we've just gotten the technology to do it right (via current levels of CGI and Green Screen). While posted recently here is an old fight between Superman and Captain Marvel from "Justice League: Unlimited"
http://www.youtube.com/watch?v=f3tmtNqG3aE
The thing is that could be done in a cartoon previously (and happened all the time in comics) but it's just been recently that we could have things like the Kryptonian slugfests in "Man Of Steel" done with real people.
Of course I'll also be the first to point out that part of "comic reality" is the lack of realistic fallout to this type of thing, this is why you don't generally see innocent bystanders getting crushed (for example there is pretty much nobody dying in the backround of the "Man Of Steel" movie), and why neither Superman or Captain Marvel wind up suffering permanent PTSD from their duel in that comic over having killed a few thousand people in light of their respective codes against killing. Of course exceptions to this DO exist. In the cartoon "Superman Vs. The Elite" civilians are apparently shown being killed in the midst of a superhuman throwdown... but it's also faked, as part of Superman making a point.
http://www.youtube.com/watch?v=zexXH3lS8Uw
Sadly the first part of the fight (where he's apparently losing) isn't up, which actually can make a case for Superman being a huge troll, but well, you know.
Understand also that this is pretty much regular comic reality, there ARE comics universes and such that DO set out to be a lot more realistic about things, and the issues of collateral damage, mass murder, and the morality of the entire idea of superheroism is brought into question. Indeed this was kind of the point of "The Authority" (DC/Wildstorm) when Warren Ellis was at the helm. Were they good guys? were they bad guys? What they were doing was necessary, but at the same time you had bits about the actual cost of say stopping a transdimensional invasion when "The Doctor" proceeds to remove a portion of the alternate earth doing the invasion from the earth's normal rotation, causing it to be destroyed and killing millions of people (along with the clear message: mess with our dimension, we'll be back). They didn't pull any real punches with that either, which was kind of the point.... but that's also not the kind of thing MOST super hero fans want to see, they want heroes to be campy to get away from you know... reality.
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That said, don't get me wrong, I'd like to sort of agree with Yahtzee on some of this, as many might know I'm a pretty extreme militant, and believe the world is both overpopulated, and that nothing gets done, especially in war, by the first world due to morality and concerns over collateral damage... as I've said many times you cannot break a people without attacking the people, not just the military... but that's an entirely different discussion.
The bottom line is that comic books tend to represent a "perfect world" of sorts where the damage is generally just for show, the good guys usually win in the very end (even if they lose battles along the way), and idealistic morality (even among dark heroes) can be maintained in doing so. Some can question how all this collateral damage can happen without killing any innocent bystanders, and people are still going to love Superman. If your going to ponder that ask why a superhero who has a secret identity, and might be "wanted" by the police even when they work with him (at least officially) and beat the crap out of some dude after committing tons of crimes doing things the police can't, and then turn him over to the authorities to maintain their code against killing, and then have that guy go to jail and all the evidence collected by this anonymous vigilante stick. Sure, in comics it doesn't ALWAYS work, sometimes the plot has the system letting a bad guy go when the plot demands it. Typically having the system work like it does in real life is intended to show "how rich and powerful the Kingpin Of Crime/Lex Luthor really is" more than the silliness of having turned the guy over for arrest to begin with (and the whole situation for that matter).
Of course there ARE comics and stuff that get away from that, and handle things a lot more realistically for "mature" audiences. Sometimes even oddly within the same continuity as more campy concepts, some people read this stuff exclusively and can't stand all the camp. Me, I tend to follow both when I read comics as each has it's appeal. Things like "Man Of Steel" might be stylized a specific way but are clearly in the camp direction... your not supposed to think about it that hard, otherwise the entire thing shows how dumb it all really is.