I personally don't really care or know if the belt should last 120,000km or not. I don't want to run the risk, even if the engine is covered by warranty. If the belt snaps, then:
*I am stuck in the middle of nowhere
*I am without a car for up to a couple weeks
*there will be valve damage
*there could be bottom-end bearing damage and it will cost a lot more and take a lot more time to remove the engine, strip it down, and have a look
So, no amount of warranty offers ME peace of mind.
It is up to you, and others, what you choose to do. South Africa has similar climate to Australia - I don't know if this matters, but the climate is very different to the UK. It is well documented in UK forums and Oz forums, that belts can snap. In Australia, Alfa Romeo specify the belts must be changed every 60K or 3 years, in keeping with their recommendations, and for warranty purposes.
I also much rather over-service my car than under-service. Some people are happy to change the engine oil every 12~15K km; I would do it under 10K, even every 5K. Some people never change the gearbox oil, but I will change it every 2~3 years or every 50~60K.
My GT has only travelled 21K km, and is 4 years old. I changed the belt after 3 years (car had travelled about 18K km). I changed the gearbox oil after 3 years. The car is serviced and has an engine oil change at least every 12 months, even if it's only travelled 5K. You can call me silly - I don't mind.