Based on the differences between the two files, I suspect the problem is or related to one or more of :-

1. The PPro2012 OBJ refers to an MTL file (pianio.mtl) whose name doesn't match the OBJ file.
   This may be the root cause of the problem if it a) doesn't exist (perhaps because Poser wrote an MTL with a name matching the OBJ) or b) it does exist but the importers for Octane and C3D don't cope with the basename not matching the OBJ.

2. The material and group names contain spaces (this isn't allowed by the OBJ spec) but PPro2010 did reproduce them (spaces in group names will lead to unintended consequences in apps that use mutliple groups for their own purposes), whereas PPro2012 has truncated the material and group names at the first space, leading to some materials no longer having a unique name and thus have been collapsed on either import or export (the same might be true for groups but they're less likely to have been left with sequential default names).

3. As the vertex coordinates are quite different, there's an outside chance that something really subtle is wrong there (with an even smaller chance that the texture coordinates are responsible).
   I'm assuming therefore that the differences in vertex positions are due to the object having been moved after import, and the texture coord differences are pretty certainly only due to rounding affects.