Actually the real reason for not granting overseas clearance is that it will push the national carriers, Air India & Indian airlines over the hill.The North American & Middle Eastern sectors are a virtual monopoly for Air India as of now.The moment Kingfisher,Jet & other private carriers enter those sectors,the government will have to undertake drastic restructuring if not disinvestment of the 2 national carriers,which anyway is inevitable.
Well there's almost alway a real reason and a stated reason why bureacracies make their rules.