It wasn't on all items, although that's certainly the impression I think they wanted you to get. Here's what I found:
"Wal-Mart Stores Inc. is going for the jugular in the holiday retailing war, announcing Thursday that it will offer free shipping on nearly 60,000 online items -- with no minimum purchase requirement.
Wal-Mart's free shipping offer, which includes most electronics, jewelry and toys, will run through Dec. 20."