Not everything is rendered on the ‘Standard’ map. It would look like a dog’s dinner if absolutely everything were crammed on there. However, there are many other renderings and you are of course free to set up your own.
Mapnik (or the used stylesheet) most probably just ignores the disused tag. You can create a ticket for it as already mentioned by Vclaw, but if you really want anything to happen try creating a patch. There are hundreds of other feature requests, some of them several years old.