Uhm... Got news for you.. If the manufacturer says 105K miles is recommended and it breaks BEFORE then, tough luck.. its NOT covered as it is a wear item and should be inspected.
Belt wear is highly dependent on how you drive, where you drive, temperature of climate and engine in general ( hot running engine?) Automatic or stick? Automatics tend to be gentler on the belt etc... Any worries, I would change it, especially if its an interference engine.
As far as the manufacturer being conservative with their maintenance requirements, you couldn't be further from the truth. The last thing a manufacturer wants it's customers to think is that the car is going to cost them a lot insofar as maintenance.
Most have gone away from belts altogether. The customers got might nasty about the expense of always having to change the belt.
On the other hand, today's belts are excellent and the rib on most of them has been changed to a more rounded one as opposed to squared off blocks which frequently broke off edges and lead to jumped belts.
I agree though on the tensioner... Change it for sure!