We do know!

Another author in Rupa's stable is going to benefit from its largesse. This is Chetan Bhagat, author of Five Point Someone — What Not To Do At IIT. The book crossed an incredible one lakh copies sales in less than two years. How much this has to do with the young Hong Kong-based banker's marketing skills picked up at IIM, and how much with Rupa's strategy of pumping cheap paperbacks into the market, we'll never know. [Outlook]

I guess this has to do more with Chetan Bhagat's skills. He had plenty of skills left unused anyway as most of his skills had not gone into the book!