Blender 'MESH' objects' vertex weights are only mapped to an 'ARMATURE' object's when the armature modifier's Bind to Vertex Groups option is enabled, i.e. ArmatureModifier.use_vertex_groups == True
The above is the default option, though to be fully in line with how Blender handles armature modifiers a check on this should be added to the SMF exporter.
Blender 'MESH' objects' vertex weights are only mapped to an 'ARMATURE' object's when the armature modifier's Bind to Vertex Groups option is enabled, i.e.
ArmatureModifier.use_vertex_groups == True
The above is the default option, though to be fully in line with how Blender handles armature modifiers a check on this should be added to the SMF exporter.