Articles discussing rape were incurring the wrath of Google.
If you attempt to visit any of the various articles once linked under TVTropes' overarching category of Rape Tropes - Rape As Drama, Rape Is A Special Kind Of Evil, or Dude She's Like In A Coma, to name a few - you won't find any of the examples, explanation or discussion you might be looking for. Instead, you will find a blank page that simply says, "We do not want a page on this topic. It does not meet our content policy."
TVTropes has been aggressively purging its article database of rape-related tropes since earlier in June, when site owner and admin Fast Eddie explained that the pages were "getting [the site] in trouble with google [sic]." From the information at hand, it seems that this was a result of Google's traditional refusal to place its lucrative ads on sites it deems explicit. For some reason, it termed that articles discussing the use of rape in fiction were either explicit or somehow promoting rape, and so TVTropes was given the choice to either pull the plug or take down the offending articles.
Obviously, TVTropes chose the latter. "There is no explanation needed beyond the fact that the topic is a pain in the ass to keep clean and it endangers the wiki's revenues, wrote Fast Eddie. "We just won't have articles about rape. Super easy. No big loss."
The Mary Sue has an excellent discussion on why this is, in fact, a significant loss - and not just to TVTropes' reputation as a comprehensive encyclopedia of fictional tropes.
The nerd/geek community right now is in the middle of a phase of self-examination when it comes to the use of sexual violence as a storytelling device in media for one, and the treatment of women and female characters for another. In June alone, the videogame industry has seen controversy flare over the Hitman trailer, the treatment of Lara Croft in the new Tomb Raider, and the disgusting reaction to Anita Sarkeesian's "Tropes vs. Women in Videogames" Kickstarter - with furor over booth babes and treatment of female journalists at E3 to boot. Removing a significant catalog of information regarding the topic and its use in fiction can only hurt this sorely needed self-reflection.
For that matter, as The Mary Sue's Aja Romano points out, it's an inconsistent purge that only seems to care if the trope's title itself references rape. Forced marriage (and thus implied rape) is still there, whereas "Mind Rape," something that has nothing to do with actual physical assault, is gone. Thankfully, the Geek Feminism wiki has volunteered to step in and mirror all data that can be recovered from the site via Google Cache. It's not a perfect solution, but it works.
Frankly, I'm not sure which party I'm more disappointed in - Google for having a policy that doesn't recognize that the frank discussion of an explicit (and terrible) topic does not equal the promotion of said topic, or TVTropes for knuckling under pressure without considering alternative solutions, such as turning off ads for the pages in question or asking for donations.
Nobody winds up looking good here.
Source: The Mary Sue
Update: It seems that TV Tropers are working on reinstating the deleted pages. Whether or not this is a permanent thing remains to be seen, but it's possible that TVTropes and Google have worked out an agreement. (Thanks, warboss5!)