Well, the
Hysterically Leftist, er, History Channel didn't exactly say
that, per se...
"Rigorous standards" of accuracy, my ass.
"Ancient Aliens" and Howard Zinn's intellectual diarhea both seem to have made the cut, happily.

According to The Hollywood Reporter, 24 creator Joel Surnow’s 8-part miniseries The Kennedys has apparently been cancelled by The History Channel after the show “was not considered historically accurate enough for the network’s rigorous standards.†The series stars Greg Kinnear, Katie Holmes and Tom Wilkinson.
I’m laughing at this, because just the other day while channel surfing I happened to notice that The History Channel is still running its rigorously accurate series Ancient Aliens, featuring theories on extraterrestrial visitations to our planet – theories explained by such noted, credible scholars as Erich von Däniken.

Greg Kinnear & Katie Holmes in "The Kennedys."
What a farce this decision is.
For the record, I know Joel professionally and am certain that he and his team have put together a show that more than merits a showing on a network that currently includes on its schedule such scrupulously accurate series as MonsterQuest, The Bible Code: Predicting Armageddon, Nostradamus Effect, The Real Face of Jesus?, Stan Lee’s Superhumans and UFO Hunters.
I've seen the trailer for this, and frankly it looks great. It also appears to be pointed and opinionated on the subject of the Kennedys (in other words, it's not entirely flattering) – but nothing out of bounds, from what I’ve thus far seen.
After all, don’t we already know that image and reality were often quite different with respect to the Kennedys? God forbid that discrepancy would actually be dramatized in a television series.
As a side note, The History Channel has just guaranteed a few more ratings points for this series when it eventually airs on another network (possibly Showtime, according to reports) – which it inevitably will.