I'll take a stab....

My perspective is that when the factors which can cause tire failure increase and the consequences of failure increase, tire choice should become more conservative to keep the overall risk equivalent.

1) Tandems are heavier, increasing loading on the tire. External forces which might be absorbed on a single (rocks, glass, etc) are more likely to cut a cord and penetrate.

2) Speeds and momentum are often higher on tandems (especially downhill, but also on flats for many teams) making flat recovery more .....interesting.... and the consequences of crashing worse (times 2).

The greater tire volume used by a tandem partially offsets factor #1. The wide variation in tire volumes used by tandems means the some teams are offsetting more of this factor than others.

We've chosen to use more damage resistant tires on our tandem to provide further margin. We like Conti 4000's on our singles, but opt for Conti 4-Seasons on the tandem. Other teams might opt for even more damage resistance and go with Conti Gatorskins.

It ultimately boils down to each teams tolerance for risk, the team just needs to have much information as possible to so they can make an informed judgement.