The Wii version and DS versions COMBINED have sold 10 million copies worldwide. The Wii version by itself is somewhere around 5 million. Which still surpasses Sega's goal of 4 million though.
Of course hopefully this means we'll see another Mario and Sonic crossover in the future. Like a Nintendo developed Platformer with the two of them, that's developed by ONLY Nintendo with Sega having no involvement in the development process at all.