A replacement value is only relevant if it has to be replaced - if I use his photo without permission in a magazine or a website, he still has the photo, no replacement needed.
While I am not denying him of the photo, I would of course be denying him of the revenue he would have earned had I licenced it from him, and would be entitled to demand that, and some more. If he had said that he would sue for $6k in punative costs, fair enough. Or even if he had said that he values his art at that price, and therefore that is what he charges for a single license.
Take Hollywood as an example, when they go after someone for illegally downloading a film they don't ask for the cost of a cinema ticket, or a cost of a DVD, they want a lot more than that. They don't however say "this film cost us £40m to create, that is it's replacement value, you now owe us £40m for downloading it".