I don't think it's fatigue, it must either be an insufficiently strong bolt or they are not torqued to specs at the factory on some vehicles. The way that control arm is designed, it kind of engages and swivels within its receptacle on the wheel hub, so that bolt's only job should be to keep the arm connected and pressed against the hub...
Anyway, in the one instance I witnessed the bolt snapped on an almost new MY09 LR3, first time off-roading so fatigue surely not a factor, and we were just riding at moderate speeds on a rutted dirt road (heading to Titus Canyon, for those familiar with the area...) On top of being stuck in the middle of Death Valley and hours away from any type of service, this is what that loose control arm did to the unfortunate guy's alloy before he was able to stop:
That will ruin your weekend.
... And all because of a stupid bolt:
The Las Vegas dealer (the closest one from where he broke down) was great and reimbursed him for every expense and incidentals, including tow, hotel stay and a new Stormer rim. At the time we all - dealer included - thought it was a fluke, perhaps a single bad bolt in his near-new car... until I started noticing several identical failures on other Disco/LR3 forums such as this one.
