They were pretty clear in the statement that Valve had people who lobbied internally for 2GD to have a second chance at hosting after previous (undisclosed) issues. Gabe called that "a mistake" now.
Yes. It appears to be the lead developer (who was the original DotA programmer for WC3) who probably lobbied for him. (EDIT: Misread James' statement, Bruno was involved in TI5, not Shanghai). Gabe comes to TI and stays pretty much the entire time - He's always having a blast taking pictures with folks and talking about Dota 2, and is an unbelievably giving and kind soul during the entirety of the tournament. So it's not like he doesn't have at least some idea of what's going on, and I am pretty sure Gabe himself really cares about TI (and by extension, the Majors).
Their TI5 host (Redeye, probably the best esports host in the world) had also asked to come and host, and Valve / Perfect World said no, even though they do have multiple hosts, and there was no "choice" between 2GD and Redeye. From all intents and purposes, it seems there was a severe lack of communication between Gabe and IceFrog/Bruno; which seems to be tied to a lack of interest in the layers between Gabe and the folks on the ground floor.
Honestly, the 2GD thing is just symptomatic of Valve's complete lack of effort (outside Gabe, IceFrog, Bruno, and the few folks who work on Dota 2) to try to professionalize the actual event, even though they claim they keep wanting to. Just like Steam - they want to make their money being the middle-man rather than being the ones in charge and running the show, even though it is their game and their show. But it seems everyone in between Gabe and the folks doing the actual grunt work doesn't give a crap, and so there are a lot of things that fall in between the cracks.
Riot and Blizzard have both given them a really good template on how to move forward with the Majors - and Blizzard has a decent balance (though I think it is going away) about third party tournament support while running major tournaments yourselves. Between the Steam security incident and Shanghai Major - it's easy to believe that Valve seems to basically have gone on complete cruise control, knowing that their fans are true believers enough that they basically can do no wrong.