Roy,
your thoughts are correct. A roller bearing is made to handle radial loads only. They do not handle axial loads very well or for very long.
A taper roller bearing will handle all loads with very little wear . A taper roller bearing is made to be adjusted for clearance or preload. A roller bearing is "as is" .
They (along with any other bearings) will not survive w/o any grease . This appears to be the caes w/the Guzzi steering head.
FWIW, GM products until ca. 1960s had adjustable roller bearings in the front wheel hubs. They were a JOKE .