What are the advantages of a wood vise screw over a metal vise screw, if any -- aside from degree of neander-ness?

My question was prompted by Woodworking Magazine's 23 July blog article on Jameel Abraham's "Deluxe Roubo" workbench, which uses wood vise screws on its two leg vises.

Article: http://www.woodworking-magazine.com/...uxe+Roubo.aspx