Sarcasm aside, this should come as no surprise to anyone who's been studying the situation in Afghanistan. In fact, a number of prominent milbloggers, including Spencer Ackerman, Andrew Exum, Kings of War's Rob Dover, and Adam Weinstein have also expressed similar mock surprise. (Milbloggers certainly are snarky bunch) Sadly enough, even this blog has mentioned the ISI and Frontier Corps' support for the Taliban on several occasions.
(The link between the ISI and the Taliban is so well-known, that some had even speculated that the arrest of Mullah Baradar, the Taliban's second-in-command, was little more than the ISI's attempt to purge the Taliban of moderate elements seeking to strike a deal with ISAF, thus lengthening the war.)
For good analysis of the issue, check out Exum, who discusses the longer-term ramifications of the Wikileaks report, as well as Adam Weinstein, who provides a much-needed primer to reading SIGACTS, FRAGOs, and other such documents.
Also be sure to also check out Seth Jones' "In the Graveyard of Empires", which delves into the sordid history of the ISI and the Taliban.
*--I apologize to Jason Sigger for stealing his signature line.
Update #1: I even brought up the issue of ISI support for the Taliban in my exclusive interview with the Great Satan's Girlfriend. Yes, you heard that right, GSGF. Apparently, she's a more timely news source than Wikileaks.
Update #2: Wikileaks already broke the story of Pakistani support for the Taliban last year, when they posted NATO's "Master Narrative" for Afghanistan. The document, protected with the password "progress", advises NATO Public Affairs Officials to remark, only if pressed for information regarding Pakistani support for the Taliban, to admit that ISAF troops had, on occasion, been fired upon from the Pakistani side of the border. Of course, we all suspected the truth.