Jacques, the porn is there, its just identified as such. Whether or not it is included in results is a function on the query.
One of the funny things about language is that there is always a 'pun' or an innuendo which can trigger a hit on a porn site, however if most of what you're looking for isn't porn then the web site has to assume you are not looking for porn and avoid some NSFW link from surfacing into your search results. You could always explicitly ask for it with /porn but then that is a clear signal of what you are looking for.
Part of the crawl data includes an indication as to whether or not the ranker thought the document was 'porn' or 'not porn', so if you're selecting things to return you can ignore that bit, mixing porn with non-porn when someone searches for 'beavers' you get a wider variety of results than you would if you were assuming you meant the furry critters which chew on trees or sports teams and limiting results to those documents.