``Digital'' here has two meanings for us. First, a key advantage of digital computation over analog is freedom from error. By factoring a large state system as the product of a modest number of two- and three-state systems, we are able to maintain good separation of states in each component, which results in a much lower chance of error than with an analog representation of the large set of states. Applying this principle to text input helps keep down the rate of misidentified characters.
The second meaning of digital for us is computational, by which we mean specifically the ASCII character set, as opposed say to an alphabet one might use in setting a newspaper or typing a novel.