Believe us, it is not a scam, although Honda belts are of very high quality with a good built-in safety margin.
I would do as the manual says, and replace it and the tensioner and water pump at the same time. Most of this cost is LABOR, hence the difference in cost quated. A good independent shop will do all this for about $750 or so.
The risk varies with the ambient conditions (extreme heat, cold, or the Pacific North West) as well as the driving cycles and numer of cold starts. Honda does not know whether you live in Phoenix or in Fairbanks, Alaska, so the safety margin has to be large.
There was a Honda owner's publication sent to me a few years back. One Civic owner bragged about going 163,000 miles without doing anything to his car (other than routine oil & filter changes), including not changing the timing belt. This is playing automotive roulette.
If you want to gamble, go ahead, but most Hondas have interference engines and a broken timing belt repair starts at $2500 and goes way up from there.