Well they all have their own web service, that's how they can deliver the interface. Of course there are a lot of applications that know they will run aside with others because they complement each other and will set a default port that won't interfere with them, but it can still happen and that's why you can change the port. 8080 (and 8008) are just the official alternative ports for HTTP traffic and thus still often set as default in the configuration of many applications.