If memory serves, the rules would kick out road bikes with cantilevers as well (touring bikes, cross bikes). I don't think it's any big deal; it's just a way of paying homage to the history of the sport. Plus it allows a bunch of middle aged people to say hey our our bikes really are cool and gives them a reason hang out with other cool kids on a tough ride. That's why I think that the while the bianchi eroica may be legal, it really subverts the whole idea of an eroica. YMMV.