I suspect the lads at Halfords may have thought that the 10 year / 100,000 mile is the second cam belt change for your vehicle as that frequency seems unusually high.
I read a report a while back that condition surveyed Cam Belts across a number of manufacturers and vehicles against their servicing schedule. If I recall, the results were: The average Cam Belt Replacement schedule is 60,000 / 6 years and that on average, a Cam Belt was found to 85% degraded when removed in accordance with that schedule.
My view is that that is cutting it close as the variables that increase wear on a Cam Belt from Cali to Cali are many, both in usage and the environment in which they are used and kept. For example: the bloke from Scotland's Cam Belt sees sharper changes in the temperature and works the vehicle harder on hilly roads, will not doubt degrade quicker than my Cali that isn't exposed to the same changes in environment in flat countryside usage in Wiltshire
I take your point about why have manufacturers not been able to design a Cam Belt that can last a lot longer. I think there are a number of reasons for that:
- Increased revenue through servicing;
- Research and development cost/effort vs the overall benefit.
With the second point, some items have to be a consumable because the material is found to be the most appropriate for its function and it is a balancing act to for designer's to get the most out of the materials in terms of performance vs degradation.
I bought a 2012 Cali earlier this year that had 45,000 miles on the clock. The seller said the Cam Belt was good for at least another year / 20,000; however, not knowing where the vehicle had been and how it had been driven, I chose to have the Cam Belt and Water Pump replaced last month as I didn't want to risk a failure and the cost associated with that.
Whilst VW may be more conservative with their Cam Belt replacement schedule, it's not something I'll take a chance with!