Those are game asset resolutions and they have to be much smaller meshes. That's a different animal than high-resolution 3D still or animation production. Even so, some games are using assets that are even denser than 17,000 polys for characters! Anytime you reduce the density of a 3D mesh, you reduce the artist's capabilities when creating something that uses that same mesh. Poser's current content market relies, almost completely, on a base mesh's ability to be morphed. Reduce the polycount and you reduce that capability - You can't move verts that aren't there. (Though, you can still use materials and such to produce certain sorts of deformations, but that's nothing near as powerful as being able to move just one vert where it's needed.)

what games use a 17,000 polycount ? are they used in the game or just for promos, video's in between levels or something ? what's the 8000 polycount game meshes for ?
you know the polycount in the biggest games ? or a clue how to found out ?

Here's one article on the issue of increasing polycounts in game assets: http://wccftech.com/ryse-polygon-count-comparision-aaa-titles-crysis-star-citizen/

As far as "how to find out" a simply internet search would probably work. Or, going to a board like Polycount or CGTalk and asking there would probably get the answer. There are plenty of in-game asset files that either get cracked or are open to mod developers that you can quick answers from just by loading them up in an editor that accepts them. There are limits to the usefulness of polycounts, though. But, that some games are starting to push what would have been "insane" polycounts speaks to the fact that some people think that the best polys are more polys... :) :D