Indians use "crorepati" for someone with a crore rupees. Interestingly, the Indian equivalent of Who Wants to Be a Millionaire" is "Kaun Banega Crorepati" (who will become a crorepati).
As for millionaire/billionaire, imo it's hard to tell but on HN I would infer USD. (Amitabh Bachchan's net worth is ~$400M based on a quick search.)