I think a lot of it comes down to marketing - it looks cool, might be ever-so-slightly more aerodynamic, and (particularly in the case of low spoke counts) might shave a few grams off the weight. Considering how much of road bike marketing and sales goes to the racer and wanna-be-racer crowd, it sells.
That marketing works because I think that the downsides, when factoring in modern rims and modern hubs, are overemphasized. I've ridden a much-used radial front wheel with a Shimano Ultegra hub with no ill effects, and I also have ridden low spoke count (20 front, 24 rear, albeit laced 3 cross) road wheels for thousands of rough, pothole covered miles around here and have only had to touch that wheelset with a spoke wrench once. That's better than I can say about some 32 and 26 spoke wheels I've had. In fact, I think I'll do 40 or 50 miles on them tomorrow.
(As always, YMMV. I can only speak for my experiences.)