Hi there,
The problem is one of supply and demand really. Suppliers may have older stock on the shelves that will require a BIOS update for an AM3+ processor to work so Gigabyte have to make users aware of this possible CPU compatibility issue, hence the warning on the product page.
If you are buying the motherboard from a well know hardware supplier/on-line retailer, then the safest thing to do is to ask them to update the BIOS to the latest version for you before they dispatch the motherboard.