A bit of interesting trivia. The akinator is based upon a premise in information theory created by Claude Shannon. Basically, if you reduce the possible user responses to simple yes/no answers, then you can represent every person/item in the database by a string of 1's and 0's - or an N-bit integer, where N is the number of questions asked. Every item can be uniquely represented by an N-bit integer.
To think of it another way, each response halves the set of candidate answers. Obviously, if you have more than two responses, you achieve greater scalability.