http://www.law.cornell.edu/uscode/ht...4----000-.html
Approval of tracks as prerequisite to acceptance of wager; exceptions
(1) In addition to the requirement of subsection (a) of this section, any off-track betting office shall obtain the approval of—
(A) all currently operating tracks within 60 miles of such off-track betting office; and
(B) if there are no currently operating tracks within 60 miles then the closest currently operating track in an adjoining State.
Betfair needs approval by at least one track to comply with federal law whether they change state law or not.