The Wii and 3DS are close enough in specs that you could release the same game on both platforms. But, this situation won't last long, since the Wii U is coming out this year.
However, the interesting thing about the Wii U is that it wouldn't even need to have separate versions of games released on the home and portable systems. With the touch screen controller, Nintendo could finally release the 3/DS Player that I've always wanted. Then, I'd no longer need to wish 3/DS games were on the Wii, I could buy them and finally appreciate them on the big screen.