Apple has started shipping a different Thunderbolt Display SKU to its stores and Official Resellers. The new SKU is largely the same as the old one, which suggests that the differences between the two products aren't going to be very substantial. 9to5Mac discovered the change, pointing out that the Thunderbolt's SKU has been changed from MC914LL/A to MC914LL/B and noting that this switch is only a couple of days old.
So, what does the change signify? Apparently, the change is due to the fact that Apple is now shipping MagSafe to MagSafe 2 converters with the Thunderbolt Display in the box. Indeed, all signs point to that as the change, with Apple's store listing for the Thunderbolt Display updated to show that MagSafe to MagSafe 2 converters are now included in the purchase price. That isn't exactly a big surprise, considering that Apple has already been providing the converter free-of-charge to those who purchase the Thunderbolt Display in its stores, and has been doing so since June 11 - now the company is just providing one in the box rather than on the side.
Since Apple hasn't outright confirmed the meaning behind the change, there's still a chance that the SKU switch could mean something different (or something more). Still, the evidence strongly suggests that the converter is the reason behind the change, and even if it isn't, the similarities in the SKUs signify that the change is nothing major.