Contacted for comment, Microsoft told us that it is "currently running a promotion in-dash that gives Silver members a special opportunity to upgrade to the full benefits of Gold membership at a reduced price for a limited time." Specifically, it's being extended to all current and new Silver accounts, redeemable via the 360's dash and on Xbox.com, and ... doesn't have a set end date, according to MS. But it is time-limited. (Love those invisible time limits!)
Some retailers, including Amazon.com, are offering physical 12-month -- actually, 13-month -- account cards for the same $39.99 price. When asked, Microsoft said that this is no indication of a planned permanent price drop for yearly subscriptions. Sony's PSN crew just smiled.