It's not about how easy the exploit is. It's not even about whether Ensidia knew.

This is, to put it bluntly, almost universally a public relations coup for Blizzard. And Ensidia's doing exactly what Blizzard wants them to do, whether they're doing it consciously or not.

Consider:

Blizzard hasn't publicly announced the ban. They know they don't have to. They know that Ensidia's going to rear up and complain about it. The people who care - the people who are gunning for firsts, the people who want to know about the fights ahead of time, the people who might exploit - now know that the top guild in the world isn't immune from consequences; why should they think they will be?

Consider:

Blizzard says "We know about this bug and we're fixing it as fast as we can." hours before Ensidia says "They need to fix this bug!" All Ensidia's doing is highlighting the fact that Blizzard's on the job. Ensidia aren't idiots. They know that an encounter that isn't tested on the PTR is going to have bugs. There's an in-game way to report bugs for a reason. In their rush to World First, they found a bug, and instead of being responsible as gamers and testing and reporting the bug, they were responsible to their sponsors and their egos and blew through the encounter anyway, and then downplayed the bug after they'd claimed World First.

Consider:

By saying "pull everybody off Cataclysm and put them on fixing this encounter", Ensidia is saying two things: "the Lich King encounter is really important and everybody should want it to be right as soon as possible", and "Cataclysm is huge, and its developers are the best at Blizzard".

Ensidia isn't even really taking heat - they just cool their heels for 72 hours and everybody rallies behind them for being underdogs. (Look at the comments here!) And Blizzard gets everything it wants - and all it took was a 72-hour ban. (Hell, I'm tempted to think that they knew about the bug and left it in on purpose.)