I suspect if the dealer "inspects" it at 4 years, and says it's fine, but it then breaks... there are going to be questions and expected cost-covering.
Much safer for them to say to replace it.
Personally, I'd be wary of running more than 5 years - the potential failure cost is much higher than replacing it. Of course I wouldn't trust the dealer to do it right, so I'd end up doing it myself!
I used to do the belt on Dads E30 325i every 5 years - it wasn't unusual for it to have only done 30K on a belt, water pump and tensioner. Of course BMW parts are far more reasonable than VW ones, too!