I think you're all just mad/jealous because they aren't disclosing how they killed it(in its entirety) as of yet. >.>
Honestly, you don't know how its "meant" to be defeated. Death has to be avoided in some manner, so devising a plan is better then doing nothing at all, and just succumbing to your early demise.
At least its been clarified though, that the /logout was to avoid something. lol I'm sure plenty of us were thinking you have to log @1% HP on PW for it to die...god that would be so dumb, but I wouldn't put it past SE. xD
My guess is they had several parties there for the fight though. Possibly to switch out PT's in the alliance so that if a PT wiped they could be replaced, and taken out of line of fire.
~Edit~
"If all individuals who have developed enmity die, Pandemonium Warden will return to his spawn point, with his train of lamps, and will not be aggressive to any non-combat action."
Can't seem to find a despawn time. :(