I think vB. org is not necessary to have a mobile friendly URL for this site because it's too popular and well known...
But vB team should have develop a responsive theme for version 3 and 4 which it is lacking for members' sites..
Google is going update algorithms on 4/21 this month and it can decrease rankings on mobile search results for sites without responsive design.
I consumed some hours to covert my forum style into responsive design, which only has on vB5