This policy came about after I encouraged interns who were 2/3rd of the way through their internship in 2012 to apply for the Foundation membership. The membership committee preferred that interns have a chance to figure out their level of participation in GNOME after the internship before applying and, as a rule, wanted to see non-trivial contributions for a period longer than 6 months.
The intention of having this statement in the internship wrap-up e-mail is to tell interns about the foundation membership and encourage them to apply at an appropriate point.
I think some guidelines there are preferable to not mentioning the foundation membership to interns at all.
I believe most interns make non-trivial contributions during their internship, but because the membership committee has further discretion about the expectations for the membership applications, we need to figure out how to communicate these in future e-mails in a way that is encouraging and relates the case-by-case provision of the bylaws.