James M over at Grognardia has an article about computers in Traveller. Star Frontiers, from that year of awesome computing 1981, suffers from the same problem.
Last year, though, I came across the concept that will reconcile the Star Frontiers computer rules with the way modern computers have far outstripped what they appear to do.
What's called a computer in Star Frontiers is an AI machine. Something like I'm using right now to type this blog post is just a piece of tech, and falls under the Technician's skills--like chronocoms, polyvoxes, etc.
If you need to reprogram, repair or deal with an intelligent machine, you need a Computer Specialist because they're just SO complex. That's also why the most powerful ones are as big as a house. It's still not very "realistic" but it seems to answer the question of why the rules work the way they do.