Nothing wrong. This is standard industry practice. Check out glassdoor salaries for companies in diverse locations.
Startups are more personal, small teams, that once in a while all of them, including the "boss", gather together to drink a beer or soda, and you know that on that table, people with same responsibilities have same compensations. It feels fair.
There are reasons US guy won't want to live in India, right? So the salary should compensate at least some part of those reasons (I mentioned in another comment here).
Most people with jobs from poor countries have to support way many family members or relatives than that US guy.