Just because you don’t like the feature, doesn’t mean that other people agree with you. Like it or not, people use Facebook and Twitter and they like having the ability to track friends with it. If you don’t want to use it, don’t use it! This is an OPTIONAL (read the definition) component that nobody is required to use at all. It is there for people who want to use it. I know tons of people that would love the ability to get easy access to their Facebook friends without going to the page and hunting around for relevant information. They would rather have native support.
Having the OS support makes using these services (like Flickr for example) easier and much more convenient and easier to use and actually saves Flickr the effort of developing something they are unlikely to bother doing in the first place.