You are correct - some assets have progressive meshes (PM) though. For commodities, it's usually a different kettle of fish entirely. I will have to check my version on that one.
Shane
EDIT: Looks like a change made by N3V/Auran in Trainz Classics (trainz-build 2.7) - it's only a warning anyway, so may be easier to ignore it.
EDIT EDIT: Looks like an empty mesh-table is sufficient:
mesh-table
{
}