OK... this is where I show my ignorance, so someone correct in the (very likely) chance that I'm wrong...
How is releasing a sequel to a game that's already selling well a bad thing? I mean, sure the current game is still profitable, but for fans of the current title who want something new, wouldn't giving them a sequel only help sales more? I don't really understand how releasing "Newer Super Mario Bros." would have any negative impact on the first game.
With that said, this is pretty exciting news; I mean, a new Mario game? A NEW MARIO game? Nintendo must be feeling rather wild and crazy if they're going to release more than one mainstream Mario game within the same console generation. I'm probably jumping the gun, but I'm calling a new mainstream game; it may either be a new DS title or a new Wii title. They can't be referring to "Mario and Sonic at the Winter Olympics" or "Mario & Luigi 3" since those have been announced since the beginning of the year.