[JH1]

I'm haven't travelled through water in mine and usual driving in wet weather won't affect them; discs would need a good submerge in cold water whilst properly hot to warp. Undoubtedly though, it's extremes of heat/cold that will cause the issue. Not sure about the torque being a cause; haven't heard that one before.
BMW now have a brake drying facility which minimally applies the brakes in wet weather to keep moisture off the disc ensuring immediate brake efficiency when you need to hit the brake pedal. I think this could likely be a cause of excessive heat and hence could lead to the discs warping if it isn't operating exactly as intended.
I'm also aware from a number of different sources, that the quality of consumable parts has declined considerably in the last 5-10 years and they just won't last or perform like they have in the past and are now prone to more faults/issues like this.
Something else to factor into the cost of ownership I guess!!
At least on this occasion, BMW accepted it was a fault/defect due to the parts and replaced them under warranty which was a decent thing to do.