As the final gearbox and brake calliper is of the same design as the bikes with cast wheels and as there have been no postings of the calliper breaking off cast wheeled bikes. Surely one must question if it is a problem with the spoked wheel design and not related to lack of locktite or axle design. IMHO.
Maybe there are just as many calipers working their way lose on cast wheeled bikes but with the consequences are worse on wire spoked wheels. The wheel failure being the consequence rather than the cause. I have probably ridden 70,000 miles on BMWs fitted with spokes and less than 10,000 on cast wheels. The big advantage of cast wheels is they are much easier to clean.