Hmm, interesting proposition. On the one hand, as potentially any 'tourist destination' could start issuing stamps for passports, we would end up with a virtually infinitely long list of 'destinations'. I believe there is another site for 'places' (towns etc.) visited, but its name escapes me.

Custom and practice sems to have established Passportstamp as operating strictly at the "Country" level, against a particular (but not the only possible valid, don't get me started), stable, well-defined list of 'countries' (, dependencies, etc.). This does change, but (I think) only when a territory gains independence, e.g. Montenegro from Serbia recently.