I don't see that pattern with these new members, the one from last generation/year had over 1k in one week, they really were post-whoring through the whole site.
For many of us it's still new and exciting so we interact on the site more.
It's like when you have a new shiny toy and you don't want to do nothing but play with it all day
It's always like this. Everytime registration opens, the new members are so eager to get posting they kind of go overboard. Probably about half of them won't even be using the forum a year from now I bet.