It should be nice to *encourage* uploaders to upload, at least, a neutral/standard file format version of their objects (.obj for example).
MAX, cannot use if you don't have MAX. Poser, the same. Both programs allow to export .obj (as far as I know). Almost any 3d software reads .obj.
How to encourage it, I don't know. I wouldn't force anything, but an "official recomendation" might work.