You can only skip the formalities if you've already been introduced.
Once you get past the cool factor of good info-design, though, you come back to the same issues of accountability and trust that haunt every discussion of media and technology. In order to present very dense information in a format that affords skimming, designers must obscure or omit some of the sourcing, details, and exceptions that would detract from the graphic's impact.
Of course, it's sourcing, and details and inconvenient exceptions that are the same credentials by which any media establishes its credibility. In this case, the publisher is assuming that the audience trusts that what's been redacted isn't key to understanding or believing in the narrative.
Part of the reason that media such as dramatic television series and weekly newsmagazines and blogs can make such assumptions is because of their episodic nature; Repeating media creates an implicit social contract that (usually) enforces trust between the creator and the audience. I know when I read a blog post that the author's going to be back at that place the next day, and that increases the odds he's not going to just lie to me. A corrections page only has value if you're making the assumption that you have a relationship with an audience that's going to know who you are, and where you are, and is willing to return and continue that relationship.
That's a risky bet sometimes, of course. I think of the New York Times as very credible, but there's some large number of people who don't, and that audience is unlikely to pay attention to subtleties about an article. That extends to relevant subtleties such as the fact that the article I'm referring to is actually an excerpt of Steven Johnson's book, and not produced under the normal editorial process of the Times, though I'm sure it still meets or exceeds their standards. (And of course, part of the reason I trust Steven is because he's got his blog where people can ask him questions.)
This is affected by issues that Scott McCloud raised in Understanding Comics. In defining comics, he uses the phrase "sequential art", because it reinforces the importance of sequence and repetitive structure in informing that medium.
Episodic or repeating content is important because you can learn from not just what's on the page or screen, but from what's between those episodes. You can fill in your own experience, or make inferences from the frequency of updates, or you can (with blogs) give feedback and comments that influence the next episode.
So that relationship, that social contract, is what allows for the complexity Steven mentions in his story. The trend he's identifying isn't that there's less crap on TV, it's that all TV, whether it's crap or genius, is more complex and more challenging and better food for your brain. And it's possible because writers and producers are willing to assume that you've either already got a strong relationship with their show on an ongoing basis, or you've figured out the missing parts for yourself, or you're willing to go and Netflix or buy the DVD of the series later to fill in the gaps you've missed.
That's the same relationship and complexity that blogs allow for with their repeating nature. I don't know that I've ever defined what CSS stands for to the audience of my blog, but I feel that almost all of you already know, and those who don't are Google-savvy enough to look it up, and those who are unwilling to do so can find out from one of the other sites they read. And in the same way, if I make an offhand joke or an allusion to the topics I fixate on for this site, I'm assuming there's a continuity to the narrative that makes context implicit. Or, you know, you can just use the search function.
What's most interesting is that, for an increasing part of my readership, this is a bad assumption. But blogs are the most forgiving medium in this regard. My readership increases at some rate which makes it likely that most people haven't read my posts from two years ago, let alone five years ago. A joke based on you having read a post in 2001 will only resonate for a small subset of the audience. (Granted, that's probably the audience I'm writing for, subsconsciously.)
But it's only with blogs thatyou can easily go back and see what a particular reference was referring to. Even better, I can just link to it. With TV, you'd have to hope it was Tivoed, or that it would be repeated, or that the series came out on DVD. With a newspaper, you'd have to drag ass to the library or, in the best case, only have to endure the drudgery of site registration to browse the newspaper's online archives. So we've got the leg up on them by letting someone start in the middle of a complex, challenging conversation and assuming that, even if you don't know the context at the start, you can go back and find it.
So we're lucky. There's nothing worse than the flashing arrow Steven mentions in his story, and there's nothing less funny than having to explain the joke. With blogs, we don't have to unless we want to. And we can still have a medium that's as complex, and as good for you, as the best TV or newspapers have to offer.