Don't compare broadband in the US with broadband here. ISPs in that specific country and a few European countries laid their infrastructure years ago. Most Indian companies are still struggling to provide last-mile connections, and those that have managed have pretty much spoiled the city skylines. Apart from Reliance which has their own backbone, all other ISPs sublet bandwidth and gateways from one or two other operators, and those are bandwidth capped in the first place. So if Airtel leases out 500GB pipe bandwidth to 'x' ISP then 'x' has to manage all their geographies within 500GB. Similar to how airlines and hotels 'overbook', ISP's 'oversubscribe', so bandwidth management becomes an issue that different ISPs have different methods to handle. My ISP sublets from another ISP who in turn sublets from another ISP. The 'master' ISP has FUP, Level 1 ISP sells by total bandwidth (one-way) and my ISP has no FUP - I pay 750 bucks/mo for 768 down/500 up.
IINM only Airtel, Reliance and VSNL/BSNL/Tata have their own fiber backbones, all other ISP sublet from them. In addition, gateways are leased by bandwidth consumed, as India has very few gateways. Broadband penetration in the country is less than 5% of all internet users, and internet users are less than 0.5% of the total population of the country. It is still a luxury item, and the cost will remain high till penetration reaches sane levels and operators look at expanding the market as a source of revenue (similar to what happened in mobiles).