they have the gist of it, its there to compensate for the fact that the mast was originally designed for a windsurfer. on some early masts I shoved some whacking great heavy pipe up there, then john and wayne built their yachts and just used the lightweight windsurfer mast extensions( not mast tops)
they then proceeded to beat me so I started making lighter mast reinforcers.
if you have none the mast will eventually snap at the mast step base, or the rowlock.
having the stiffener in the mast also led to gradually shortening the mast step from the original 500mm down to 250mm