Price matching. If you go to another store that sells the 233 and point to a Walmart ad with the 231, they don't have to match the price. Best Buy does this all the time. IIRC when Pioneer plasmas were first being sold at Best Buy, a model number was, for example, something like 5041 where everyone else was selling the 5040. This way Best Buy could claim it was a different model, and they didn't have to match someone else's price.
SMK