Renderosity is much more than just the Poser forum. And there are many folks posting renders and photos besides going through the marketplace. The DAZ forum I believe is just showing members logged into the forum which has a lot fewer sections than here. It's not an equal comparison.

Both renderosity.com and daz3d.com have a Google PageRank of 5 out of 10.

renderosity.com has 90 quality backlinks according to Google.

daz3d.com has 204 quality backlinks accordng to Google.

Both sites are spidered all the time by Google.