The Wii is made to work with any setup you throw at it. Being setup standing with the stand, or without the stand, or sitting flat as well.
If you actually setup the Wii without the stand and look beneath it to see how much space there is left, and then put the stand on and check the space as well, you will notice, there is the exact same amount of space for the air to circulate from the Wii.
Plus, it just looks better without the stand in this setup.