I don't know if they are mostly introverts, or if it is just that a lot of them are socially awkward. There is a high incidence of disorders like Asperger's Syndrome among computer professionals. That can be mistaken for introversion.
I would have to agree with you on this. In a way, most IT professionals are socially awkward. I had a friend working in this field once comment that his girlfriend kept on complaining that he was so much into his career.
I do not know if the same can be merged with being an introvert?