Why does Google use ww instead of www?

Is there a reason for using ww instead of www?

[arnarn]

I recently ran across the following [ww.google.nl...]

Is this proper form? and if so, is there a reason for it?

[tedster]

They set up both versions to resolve - to accommodate typos I assume.

[arnarn]

seems reasonable, thanks.

Since they do it, do you think everybody should do the same for their website(s)?

[zCat]

It's not a bad idea; you just have to make sure you do a 301 redirect to avoid duplicate content problems (which google presumably doesn't have ;-).

I usually set up ww. and wwww. to redirect to the www.-version of my sites.