I have read that it was often practice to put a tight fitting broom handle piece through the steering tube for strength. I heard that was more so for professionals and serious riders, and that the broom handle acted as a damper for vibration as well.

I have also read that wooden plugs and corks were put on vintage bikes that had oil poured into the steering tube to keep the bearings lubed. Some bikes have an oiler hole with a little plug and even a screw on the steering tube. I have seen pictures of many plugs that were oil soaked. Scroll down to the bottom of this link: http://www.43bikes.com/specialissima.html

Perhaps it also did help to keep mud and such out.

A few of my bikes and old pictures on my Flickr page:
http://www.flickr.com/photos/umpire54/sets/