Aren't most of the characters in The White Tiger rather stereotypes than "real", complex characters?
You make a very shrewd observation with this question. In a sense, the characters are used in this novel to show certain aspects of modern India, and therefore, because of this quasi-allegorical usage, they are presented as stereotypical characters rather than fully psychologically developed entities.
A good example of this would be Mr. Ashok, Balram's boss, who represents new and more liberal ideas after his time in the United States. However, both he and his wife find that they run into problems when they try and implement those new ideas. To give one example, Mr. Ashok constantly bemoans the way in which he is forced to bribe, but it is something that he engages in. His vision in the novel is shown to be too simplistic and unable to really tackle the massive contraditions and inconsistencies that are shown to exist within India.
Likewise, Ram Persad, the number one driver in Stork's house, is used to show the pervasive strength of caste and how important it still is. Let us remember that he has exactly the same job as Balram, except Ram Persad believes that his higher caste makes him better than Balram. Even though India is presented as a country that has advanced in some ways, it is still mired in traditional notions such as class that hold it back in others.
To some degree, the characters in White Tiger are stereotypes, as they are supposed to represent a tale of greed, corruption, and violence that characterize modern-day India. Balram Halwai, who starts his life with only the name "Munna," or boy, writes to the Chinese Premier, Wen Jiabao, to explain his rise from poverty in what he calls the "darkness" of India (referring to the poor interior) to a position of wealth in Bangalore (which he refers to as the "light").
Balram wants his story to serve as a kind of example of the everyman in India who achieves success despite the greed of his stereotypical Indian bosses, Mr. Ashok and Pinky Madam. These characters are stereotypical in their unrelenting greed and superficiality, but Balram has some depth to him that makes him more than just a stereotype. For example, the retelling of Balram's experience watching his mother's funeral along the Ganges makes Balram a more rounded and less stereotypical character. The reader understands Balram's desire to make more of his life after seeing the poverty and deprivation in which he grew up.