Pardon me, but I'm a little flabbergasted.
...
Or are these people just blowing off their training and not buying computers because they don't want to waste money on something they don't use anyway?
You are being paranoid. If I were on a cruise with all my gear back home, and had a 2-tank boat dive with DFB on my Bonaire stop, I wouldn't have a problem not renting a DC and "just staying with the guide". Of course I've dived with them enough times to trust their DMs to not try to bend their customers; I may not be as trusting with other ops in other places. Also of course I'd be sailing away in the evening and not diving in the next 24 hours.