numerous characters abbreviated the word computer as 'puter in everyday speech

This sort of observation requires very careful listening. We tend to fill in blank spaces in the sound stream according to what we expect. <Computer> => <c'mputer> is a small step. The <m> will then easily merge with the <p> and the <c> being unvoiced will easily become inaudible. Since we are used to these processes occurring we will easily fill in the sounds in post production audio centers in our brains.