Hmmm... I disagree that invading Iraq was so clearly the correct decision to make at the time. I see where you are coming from, but let me explain why I'd hold Hillary to a higher standard.
Yes, it was a product of our non-deliberative government and echo chamber media that the average person heard only arguments in favor of the invasion, but even at that time, the lead up to the war and the justifications that were made were highly broken. Recall the premature ejection of the weapons inspector, their assertions that there were no weapons, Joe Wilson's repudiation of the attempted yellow cake purchases, the lies about the aluminum tubes that were immediately debunked... and on and on. If one was willing to dig a little deeper, there was plenty of information to indicate that the war was dubious from the start.
Now, I don't blame any average American for trusting the information and the points-of-view that are communicated by the mass media-- though hopefully everyone will be more skeptical in the future-- but I do hold someone in leadership to a higher standard. If you are going to cast a vote to authorize war, you better damn well take it upon yourself to question the spoon feeding. Isn't this what government leaders get paid for? And it wasn't like there wasn't help: there were always people screaming that this was a bad idea, but they somehow got completely marginalized via the usual name-calling and ridicule.
Intellectual laziness and susceptibility to propaganda aren't particularly traits that incline me to vote for the next President. I don't think that an apology makes these failures go away, but it at least expresses a recognition of what happened and the real danger it presents. The systemic ability to easily manipulate the world's superpower into a silly war is in my book at least as great a threat as Saddam ever was.