Nokia warranties are only valid in the country of purchase with a exceptions such as Europe where the warranty is Europe wide. In your case the warranty will not be valid in India.
Not that I am aware of. I don't speak for Nokia, but I thionnk their reasons are as follows. Even though phone variants may seem the same, they are localised for individual countries and markets, due to defferences in languages, frequency bands, etc etc. The manufacturers would prefer you buy the phone best suited to your locality. You will find all the major manufacturers have the same policy.