In support of what Jar546 said, I was taught to use the dive tables as part of my OW classes but my boyfriend was only taught to use a computer. After my course I sat with him and within 5 minutes taught him how to use the table and he was so happy to have gone through it because the computer provided no explanations and it made him appreciate more the relationship between dive times, depth and surface intervals. I had to pry the thing out of his hands!
It's great that learning to use the tables helped your boyfriend understand what the computer is doing. However, all that tells me is that the instructor didn't do a good job of explaining what the computer is doing. If an instructor explains how the computer algorithm works, there's nothing that knowing how to use a table could add to a student's grasp of the concept. What's the difference between seeing pressure groups going up and down on a table as a function of depth, time and surface interval and seeing a bar graph get longer and shorter on a computer (or some other educational simulation) as a function of depth, time and surface interval?
Maybe the best argument for continuing to teach tables in OW class is that many instructors don't know how to explain what the computer is really doing in a way that students walk away with an equivalent understanding of the concepts involved.