<< The OP states that the manufacturers service interval is 112,000 miles (probably a conversion form 180,000 km) and I am pretty sure they know a thing or two about the engines they manufacture. >>
The durability of belt materials must be pretty well known by now, but when a new engine is designed I doubt that many prototypes will have been tested to belt destruction. The working life of a belt must depend on several factors, such as the amount of flexing per revolution (which will vary with number of pulleys etc) and the vigour of every snatch with starting and gear changes - i.e.the kind of life the car has led (stop-start may contribute here).
The safest way to avoid serious belt damage is a non-interference design of engine. I guess the makers assume a service life for a car of 10 years, so a decent belt may well last that long.
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