No problems with my disc - they are nearly maint free. But, I don't ride on beaches or on salted roads, which are probably worst case for braking systems.
If its bad on disc, it would be worse on rim brake system - where you could potentially be replacing a wheelset due to rim wear-thru.
In the example you cited, the biggest problem here was the guy who bought the $4,000 tandem failed to budget and install some $25 fenders and f. mudflap. I bet he owns some by now.
Fenders and mudflap are a good investment - pay for themselves many times over in extended drivetrain life, reduced frame damage, and less frequent clothing laundry.
Would you drive a car with no windshield? Well, you might, but not for long or very fast - unless you have goggles.