David Combs - The key point is betterment, as you point out, but I think your definitions of omissions and errors are not quite on the mark. I agree that an omission is information that should have been included but wasnt. I agree that an error is information in the documents but incorrectly stated. However, either an error or an omission can lead to financial liability for the architect, depending on how much is attributed to betterment, and when the mistake is discovered.
The AIA Handbook has a great example of this with various scenarios involving a door for which the architect has negligently failed to specify a required fire rating. The architects liability ranges from zero to several thousand dollars, depending on the circumstances of the scenario. For example, if discovered during shop drawing review, prior to the purchase of the door, the difference in the cost between a non-rated and a rated door is considered betterment, under the theory that the owner would have had to pay for a rated door anyway, so the architect has zero liability. If a non-rated door is already installed when the mistake is discovered, then the architects is liable for the installed cost of the incorrect door and labor to remove it. The cost of the fire rated door is on the owner: labor and installation are already in the contract, and the difference in cost to upgrade to fire rated is part of the change order.
Consider this omission: an egress door was required but not shown at all on the documents. The wall is built when the omission is discovered. The owner pays for the total cost of the door, and the labor to install (betterment) and the architect pays for demolition of the wall and for relocation of anything within the wall that is in the way of the new door.
David Axt A few years ago, a certain governmental agency wanted to institute a policy that would require architects to pay for all change orders over a certain % of the job cost, regardless of reason for the change, owner change of scope excluded, of course. But included were things like concealed conditions, material escalations, and traditional betterments. Needless to say, the a/e community went up in arms in protest, and the policy was never put in place. One of the issues that was brought up at that time was: if we are paying for cost overruns, shouldnt we get the savings when your projects come in under budget?
Nobody was willing to go there, of course. Johns point about better cost estimating is well taken. If owners require architects to pay for overruns, then it becomes in our best interest to estimate high, rather than accurately. And that strategy would seem to be against everyone elses best interest, not to mention the best interest of the project.