No, I didn't miss anything.
In fact, in 2006, I looked into company policy prior to our trip. The written policy that I saw stated that overnight camping was not allowed. To my knowledge, there was never a change in company policy.
A LOT has changed at Wal-Mart since I quit in 2008. It is highly probable that the policy regarding overnight parking has changed, as well.
I worked at two different stores. One store allowed it; the other store didn't. In both cases, it was manger discretion and had absolutely nothing to do with local laws. And, no, the RVs weren't affecting parking. The store manager was just a jerk.
The wording in the FAQ is done very well. It leaves the store with the opportunity to not allow overnight parking even if local laws allow, while still keeping the company as a whole in the clear (i.e. The individual asked to move is only mad at that store in general and not the company.).