There's no way in hell you launch a Beta and in a matter of days amass all that content.
What's more likely is that Envato contacted dozens of artists, photographers etc in advance and formed up their content before they launched. They've probably been accumulating content for the past year. Either that or the accounts are actually Envato staff and Envato has brought in the content from elsewhere.
It is actually the sensible thing to do, as you launch with your content rather than launching then waiting for people to submit content.
Edit: 40,000 of their files come from one guy.
This post has been edited by brightonmike: 21 September 2011 - 01:05 PM