The way that I read Jeff's comment was not so much as a ban of the Feds but he seemed to be politically cautioning the attendance of Feds on potential hostilities from attendees who aren't particularly thrilled with the recent disclosures.
We can all argue the maturity level of the conference but in the immortal words of Friedrich Nietzsche:
"Madness is rare in individuals, but in groups, parties, nations and ages, it is the rule"
Surely there would be severe consequences on both sides were there to be pranks or aggressions on Feds in attendance.
Of my many years of attendance, I have never considered Defcon to be a completely open environment free from danger, but rather a Hackers Mos Eisley where you can interact with all walks of life, but that you had better be aware of those who do not like you.