https://docs.google.com/document/d/1B061Rs4gw4zkCec35Q5v2r576e_Jd6pJfrT_5_GZ74I/preview
Sheds a lot more light on the issue, if you're invested enough to read 17 pages.
tl;dr
James was hired, and told to 'be himself' by none other than Icefrog. Valve decided they didn't like James' on camera persona, and fired him, there may or may not have been some personal vendetta's/past grudges involved with a Valve employee named Ali. As far as James is aware there was no off camera incident that could have caused him to be fired, most likely it was because he was taking shots at players, (Waga/Singsing for the final session, both of whom James claims to be good friends with). Either way I would argue it's not what he gets for "being a douche" as Valve knew who they were hiring, and what his particular hosting style is, not to mention the extreme unprofessionalism of Valve asking James to hold off on his statement until the morning, while in the meantime Gabe Newell issues his own statement during the period they asked James to cool off for outright calling James "an ass".
Coupled with the fact that he was carrying the shit out of the entire panel, and managed to come up with hours of content while dealing with the shitshow that was the production of this event and the endless delays it caused, as well as the fact that he is extremely popular among fans I'd say Valve seriously dropped the ball on this one, and for a company that is notorious for their bad PR it's sure something to fuck up beyond what anyone expected.
I'm sure Tobias will probably write up something later that puts my short shitty rundown of events to shame, but I'm about to go out so I've rushed this a bit, and I cba to check over what I've written.
tl;dr;tl;dr
The only thing Major about this event is how much of a Major fuckup it is.