1. No, driveshafts are not a service item.
2. I don't see the forum filling up with driveshaft issues.
3. As above
4. I think you've just been unlucky.
The driveshaft actually consists of a few different parts. Usually a shaft of solid metal (that doesn't usually break, as it's pretty thick), and a couple of CV joints to transmit the drive from the gearbox, to the shaft, and then onto the front wheel. CV joints have a several moving parts and are susceptible to wear, especially if the rubber boot splits and lets out the grease, and water/dirt gets in. This part is much more likely to fail, and is quite a common MOT failure across all makes and models. Certainly not specific to VAG!
Did the shaft actually shear? This is quite rare, I've seen them go when rusted though - sometimes water/salt collects around a rubber damper and corrodes the shaft until it's weak enough to snap. Another point of failure would be the CV joint seperating, although I'd expect you'd hear a lot of noise before that let go.
Ultimately, I don't think you have anything to be concerned about.