The need for a fairing depends on the cross-sectional area of the bicyclist while riding. The minimum cross-sectional area would be flat on his back, feet forward, staring up at the sky. The maximum cross-sectional area would be straight up 'n' down (similar to a DF bicyclist). All the recumbents compromise between these two extremes.
Having looked at pictures of the RANS Stratus and the Easy Racer, following Jeff's assertion that these bikes benefit the most from fairings, I see that on these bikes the bottom bracket lies below the rider's waist. Whereas on some bikes, like mine, the bottom bracket lies in front of the rider's waist, reducing the cross-sectional area. Thanks for pointing that out, Jeff.