Also, they will advetise on other boards.. Chrissy Gordon, for example, is on massage republic and punterlink.. Twitter is another form of marketing, as is AW.. Using twitter (and probably instagram for some) is a way to get their names spread..
THere are many WGs on AW with websites, too...
I find the more fancy the website, the more expensive they are, but, as GH points out, cost isn't necessarily correlated to service. In fact looking at the first 4 on your list, I wouldn't touch them with a barge pole, even if they were free (well, maybe free.. and then, only wiht a barge pole ;-))