It's standard practice for MS, they do this as a perk for the folks who fork over the cash for a Gold account. It will be available to Silver members in about a week or so.
If you really can't wait you can buy a 1 month Gold membership for $8-9 (I forget exactly how much). If you don't have a credit card, just go to Best Buy/Circuit City/Gamestop and buy a 1 month prepaid XBL Gold card.