You can call it a characteristic or call it a design flaw, either way, its not a safety issue so there is no way they will buy back your car in arbitration. I agree this should not happen in a $50K car, but at least Lexus is trying to fix the problem unlike other auto manufacturers.
I must agree with stinky pete, the cluck was not that bad. I guess some people have it worst than other. Maybe yours is really bad. Anyhow, almost 100% of people who had this lastest TSB done have not had the cluck since. As far as I know the 07 should have the latest TSB in it, I am wondering how well inform is your Lexus dealer.
This TSB is the real deal, get it fix and you can complain here afterward if the cluck comes back.