The problem with watches is that it's almost impossible to determine replacement value, unless it's a pretty recent piece. You can't use MSRP, because in many cases people pay way over that to get a popular piece (think any Rolex or a Moonswatch). In the case of Vintage, it's value is so far removed from what whoever had paid for it back then. There's also the element of seasonal popularity (this year it's popular, next year it isn't). Lastly, many of these watches are purchased on international auctions (most of mine are) for less than what they're worth new, how would you determine replacement value on that? My recent Tag is a classic example - I paid 25% of what it's worth new because the seller thought it was broken and couldn't figure out how to open it to replace the battery (it's an automatic, it doesn't use a battery - it just needed to be wound up).
So how do you determine replacement value? Outside of that, many of us are collectors - items in that collection doesn't leave the house, but should still be insured under all risk as far as an insurer is concerned. This discussion frequently comes up on international forums and it seems the consensus is that most people simply just don't insure them.