Oh no, he passed a referendum doing away with Presidential term limits! DEMOCRACY IS DEAD.
And if this vote is illegitimate because exit polls were off by a bit, the past three United States presidential elections were also illegitimate. Chavez is hardly a saint, but he's not some of authoritarian despot.
No one's arguing that the vote wasn't legitimate. People are, however, arguing that the vote isn't fair. The way you win votes in pseudo-dictatorships like Venezuela or Russia is by controlling the media. Venezuela is somewhat less blatant about this than Russia is, but it's still pretty bad.
And yes, the fact that this passed is a symptom of Venezuela being an illiberal democracy and is likely to cause it to remain so for a while.