Feature parity? When I visit that website, I don't see: buttons, wells, tables, alerts, form elements, nav, progress bars or modals. Those are all things I use from Bootstrap, and that I cannot find on Zurb's website. Maybe they are all there and I just don't know where to look.
I have no idea who @fat and @mdo are, but their lack of being behind Zurb is certainly not the reason I haven't used it. The reason I don't use Zurb is, that every time I've seen someone mention it on HN, I visit it and see nothing but a grid.