This means you can see if the games are generally considered to be for the hardcore or the casual player, how much time people generally spend on one session of the game, how much times they've started up the game, and if the game is considered best played alone or with friends.
For some strange reason, Japanese users can also see the total amount of downloads each Wii Shop title has, while North Americans can't. However, you can get a rough estimate of the sales by doing the maths with the "average time played per session" and "total sessions" numbers. The sales numbers are not worldwide, only the Japanese sales.
This feature is currently only available in North America and Japan. We predict Europe/Australia will receive it sometime later due to the fact they got the Nintendo Channel later as well.
Thankfully someone is already compiling the VC & WiiWare game sales in a nice ordered spreadsheet so we don't have to. Feel free to email them and add your own findings.