I thought the main thing about ostracism was unofficial collective punishment by the pack. The more official punishment gets dished out by a higher power (scammer label, separate forum, banning, etc.), the less I feel inclined to give them a vigilante helping of my own.
In order for a punishment to work, you have to know you're being punished.
What REALLY would be nice is: If you get ignored by somebody, on every one of their posts you see: "This user is ignoring you, replying to their post is of no consequence to them since they won't see it." Then again, that would also encourage trolling and flamebait... this is harder than I thought.