There must be some huge arbitrage opportunity to be exploited here. I mean 13% is not bad at all, take away 3% for fees and 3% for currency exchange fees... You're still pocketing 7% per trade.
Is there some sort of restriction that doesn't allow the outflow of rupees in the country ATM? I don't think so.
It is not as easy as it sounds. Physical cash is in short supply. If you are selling Bitcoins, then you have to accept bank transfer in return. And right now, the RBI is monitoring all the transactions above a certain threshold.