Air law and equality acts aside, the captain still need to be careful about not falling foul of the increasing raft of legislation both in the EU, US and elsewhere regarding "Passengers with Reduced Mobility" (relevant bits of which nowadays often are contained within most Airline's Ops Manual)
In any event for example REGULATION (EC) No 1107/2006 of the European Council states (amongst any other things...):
Disabled persons and persons with reduced mobility should therefore be accepted for carriage and not refused transport on the grounds of their disability or lack of mobility, except for reasons which are justified on the grounds of safety and prescribed by law. Before accepting reservations from disabled persons or persons with reduced mobility, air carriers, their agents and tour operators should make all reasonable efforts to verify whether there is a reason which is justified on the grounds of safety and which would prevent such persons being accommodated on the flights concerned.
Full text is here, Article 4 might be of interest:
http://eur-lex.europa.eu/legal-conte...6R1107&from=FR