AFAIK the lack of a path part is allowed in an HTTP URL per RFC2616.

       http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

> If the abs_path is not present in the URL, it MUST be given as "/" when used as a Request-URI for a resource (section 5.1.2).

Browsers may differ on whether they auto-fix schemaless URIs, but they're all required to fix path-less URIs. So it's much "safer" to use them.