Noticeably unlike to Apple iPhone Google Nexus is "Unlocked" GSM phone sold and shipped by Google only.
Moreover, unavailability of 3G Mobile technology in India could be strong reason for Nexus phone unavailability, as at present its with BSNL only. Ironically, countries like UK had already made trials of next generation 4G mobile broadband technology.
Question - Why Google didn't approach BSNL? as its also 3G and GSM phone operator in India.
However, India has its own Jugaad of getting Google Nexus by - shipping it to India (US$529 + $60 shipping + import duty = 32k INR approx.) or can also get it from ebay once people people start to resale it.