Of course, it is not. Postcolonialism, quite simply, is a way of reading – a way of reading that allows us to discuss the mechanics and features of both the colonial project and the colonial experience.
Unlike literary theories, Postcolonialism does not make any claims or require any particular structures or understanding to be in place in order to function (other than the observation of an imperial encounter of some sort). As such, it is merely a useful (but highly contested) way of organizing the critical focus of a reader. It tells the reader to pay attention to, say, the colonial encounter – but it asks the reader to consider how the encounter functions.
In short, Postcolonialism is not really a theory at all. It is merely a way of reading that draws from other discursive terrains (most commonly Marxism, Feminism, and Post-structuralism) which, when brought to bear on a particular text, allows the critic to explore something of the complex fabric of connections and interactions that describe the pre-colonial, colonial, post-colonial, and/or neo-colonial (!) experience.