DWARKA, India — Shubhrangshu Barman Roy and his childhood friends are among the winners in India’s economic rise. They have earned graduate degrees, started small companies and settled into India’s expanding middle class. They sometimes take vacations together and meet for dinners or parties, maybe to celebrate a new baby or a new business deal.

Yet in August, Mr. Roy and his friends donned white Gandhi caps, boarded a Metro train in this fast-growing suburb of the Indian capital and rode into New Delhi like a band of revolutionaries to join the large anticorruption demonstrations led by the rural activist Anna Hazare. They waved Indian flags, distributed water to the crowds and vented their outrage at India’s political status quo.

“I could feel that people really wanted change,” Mr. Roy, 36, recalled proudly.

It may seem unlikely that middle-class Indians would crave change. They mostly live in rapidly growing cities and can afford cars, appliances and other conveniences that remain beyond the reach of most Indians. Theirs is the fastest growing demographic group in the country, and their buying power is expected to triple in the next 15 years, making India one of the most important consumer markets in the world.

But buying power is not political power, at least not yet in India. The wealthier India has become, the more politically disillusioned many of the beneficiaries have grown — an Indian paradox. The middle class has vast economic clout yet often remains politically marginalized in a huge democracy where the rural masses still dominate the outcome of elections and the tycoon class has the ear of politicians.