Yeah coinbase is a trader where they purchase bitcoins and sell bitcoins. Not a real exchange which matches the buying and selling orders.
Sorry? You mean Unocoin on large scale backed by private investor to always provide market? Woah! They would have earned fortunes considering volatility of Bitcoin so far. Any ideas whether buying is manual, semi-automatic or fully automatic? I wonder what hedging strategies they use.
Maths everywhere! 
Um, i did not understand what you are talking about. How did Unocoin come into picture here? We do not have any such private investor. Buying bitcoins is semi-automatic - there is a small manual process at admin end where they approve the receipt of INR to bank account and then the order is executed. No external hedging is done but the buyer orders and seller orders usually will take care of itself every few days.
