If you buy either game from the eShop and register it on Club Nintendo, you'll get a free download of Donkey Kong: Original Edition, a special version of the NES Donkey Kong that has been edited to add the "cement factory" level. It's previously been released only with a special Wii bundle in Europe and with Japanese New Super Mario Bros. 2 purchases.
Neither of those games seem like particularly natural lead-ins for Donkey Kong, but at the very least, the offer will sway some people who planned to buy one of those games anyway, and will now choose to do so digitally.
Update: The deal applies to more games than Nintendo chose to mention this morning. Style Savvy: Trendsetters, Professor Layton and the Miracle Mask, and Paper Mario: Sticker Star all give you access to DK Original Edition if bought digitally and registered before January 6. Thanks to reader Thomas for pointing that out.