Niels Bakker <niels=nanog@bakker.net> writes:
AMS-IX does not, nor does it require its members to peer with anybody
(including the exchange-supporting network infrastructure). AMS-IX
believes that the decision to peer is up to the individual members.
NIXI (http://www.nixi.org) - the national internet exchange of india - seems to enforce a mandatory multilateral peering policy (though their policy, and their setup, sure sounds like a godawful mess, right about now) 
Quoting from their membership agreement (a word doc at http://www.nixi.org/NIXI%20T&C_%20ver_%202.doc) -
Peering Policy of NIXI
NIXI has adopted a Multilateral peering policy . Member ISPs shall
not refuse to accept traffic from other members.
--srs