Its still a persistent myth, whereas the truth is that horses hooves benefit from roadwork, as long as they are healthy, as it provides great stimulus to the frog and digital cushion and actually promotes hoof growth.
The big worry for owners is usually "Will my horses' feet wear away?!?!!" Often they will be told that roadwork is the reason shoes were invented - and that without shoes their horses won't cope.
However, during Ride Bare, our long distance trek from North Wales to Exmoor, our horses were covering 18-23 miles per day and the vast majority of that was on stony tracks or roads. Normally, we do less roadwork than this, although several miles per day is commonplace for the horses here.
The reality is that a healthy horse's hoof will grow more than fast enough to cope with this level of wear. Its probably true that if your horse was regularly covering MORE than 25 miles PER DAY on roads then his hooves might not be able to cope - but then again, probably the rest of his body wouldn't either ;-)