Why? What purpose does it serve to have a logo on a home page be a link back to the home page?

The only reason I can think of is consistency across the rest of the site.

I take that back. I thought this was about a clickable logo in general--not about the homepage specifically.

I guess it is ok to not have the logo linking to the homepage from the homepage itself. (Though there are certain sites that I like to have open and click on the logo to refresh the content.)