Why? What do you "think" it is? There's no conspiracy here.
The number after the WWW is merely a header extension to a redundant server serving the same domain.
There's a whole bunch of technical resource pages on the 'net that explains it fully (did you look?). Just google
"What is WWW6?" or
something similar to get a screen full.
Here's a simplified one for 'ya:
WWW#.x.x explanation.