Super-guild has already cleared Naxx

[Swiss Mercenary]

For an easy instance there sure are a lot of people that never managed a single boss in BT.

Attunements, and the "Have you gone through Tier 5?" gear check most guilds expect in recruits.

And past 3.0, the only reason for someone to not have seen BT would have to be lack of motivation (Or, I suppose to be exact, lack of farming Heroics/Kara for badges). There were 5-6 PUG groups a week doing it on my server. If you were fully badge geared, you could have gotten in no problem. If you weren't, you could have done a few ZA runs to fill in the gaps.

There's almost nothing in BT that required much thought, with the exception of lol Supremus (And he's killable with half the raid dead under volcanoes), Mother (Where, post-nerf bad play can be compensated with more SR, or more DPS), and Council (And I'm not going to say Council is an easy fight.)