The vast majority of UK riding is pretty tame in comparison with alpine descents, on scales of speed, technicality and duration. In theory all riding should be the same, but in all honesty most of the UK riding is what I call general trail riding - trail centre-like stuff, boring motorways interspersed with technical sections. Alpine descents generally are tough, technical and hard from start to finish. Things break due to descent duration, continuous vibration etc. Most people dont have access to the sort of scottish descents that equate to similar to alpine ones, and certainly wouldnt do 18 times round it. Other than wearing out, here's my list of breakages when mountainbiking:
Home, nearly 18 years of riding:
1x Wheel - incident with a large rock.
1x Bars - caught a tree with bar-end.
2x Tyre - glass.
1x Rear mech, embedded in a wheel, which needed re-lacing.
Alps, 6 weeks total:
Cranks - two pairs, inc carbon cranks which snapped during a drop on a downhill course.
Big ring - mawled by a flying rock.
Front wheel - demolished on a root.
Brake pads - numerous.
Rear Shock - blew seals on last run of the day
Hope Mini - overheated rear caliper and damaged seals
Front forks - seals failed.
Freehub - pawls chipped, slightly odd - possibly a fail anytime item.
Punctures - countless.
Tyres - 2, ripped sidewalls.
If you attack alpine routes slowly then sure, its no different to the UK, but in the UK your average speed is a lot lower. In the UK you may do 30mph for 10 seconds, slow back down and corner etc, in the alps you have 2 mile stretches of 40mph, followed by 20-25 for 30 second batches too and fro between switchbacks. Average speed is higher, average impact speed is higher, meaning forces are higher on average.