Most of the regular posters have their own websites or use Webshots or similar facilities.
Google is not a newsgroup provider, just a carrier for the Usenet system, MSN groups and Yahoo groups are set up as an alternative to Usenet. There is also a binary group as well for restoration/preservation stuff.
So, you have up to four or five choices of where to go for your pictures, and most of us simply don't have the time to jump between groups to find something.
If someone has something interesting to show, he just posts here and we can go and have a beak if it is of interest to us, without loading the system with large image files.
Quite web stuff is OK (after a fashion) but it is "pull" not "push". News just arrives here with no action on my part, web sites I have to pro-actively remember to go an look at and the chances are there is nothing interesting there so I've wasted my time and bandwidth.
Some members of a (closed) mailing list I'm a member of recently wanted to switch to a web based "forum". These like google news yahoo groups etc are terribly slow and just out of interest I checked the ratio of content to data shifted. For 10k of content (about 10 to 15 ordinary messages) around 500k of data passed over the link for all the eye candy...
Quite, I don't want to be forced into downloading images whilst just quickly (ha, thats gone out of the window when there is a lot of images about even on BB) checking a list.