You know, a lot of this is platform specific. No one is going to think a human figure in Bryce (or Poser) was modeled by the poster. In Max, Lightwave, or Cinema, however, it could be an original model, so mentioning it's Poser is a good idea. At arch viz sites, purchased models are routinely used, and no one mentions the modelers unless someone asks where they can find it.

I give away a lot of my wonky models, and don't expect anyone to list them, unless they use a lot of them to fill a whole room. Then a mention would be expected. Finding them on sites for sale is not tolerated, though. (No redistribution is my only restriction.)

Sambucus, the people we get irritated with are those who snag a free scene, hit render, and take all the credit without mentioning they did virtually  no work. Sort of like me taking an Orbital render, and using it as a background for a cube. Oh, great. Now I want to render a cube and paste it on an Orbital render just to see what it looks like. :X