That's just because fanfic anticipated the epilogue too much, really.

The huge difference between the epilogue and fanfic is in how Rowling did not overdo everything and kept it short and to the point. She resisted the temptation of bringing about huge developments in her world building or matching characters (as many obsessed fans wanted to see.. .Neville with Luna and so on, or give the name of Draco's wife etc.) or even to magically resolve conflicts (why on earth should Ron/Harry should now like Malfoy?), or reveal the fate of everybody (what happened to McGonnagal, Neville's grandma and whatnot). It was never what her series was about, those huge developments (even Hermione's quest was going against the nature of the house elves, for example, and the goblin's treason was another sign that not everything is black and white). Voldermort was a threat a certain order (the balance between the wizard world and the Muggle one so they could co-exist, for example) and to traditional values (like family, friendships) and the epilogue essentially demonstrates that Harry's victory did bring those things back, which was its purpose. He never fought to revolutionize the wizard world and throw away its traditions and wisdom, it's Voldemort who did. She finally gave Harry a family to love, the very thing he always wished the most deeply to have. And yes, the bonds of friendship have endured - Harry and his friends get the chance to live what his parents couldn't, and also that he met the challenge of giving to Ted Lupin, the orphan, what he didn't have himself. And yes, the Houses are still there - bonding very different wizards together as one school. Rowling demonstrated the excesses of the House system had divided her world, not that the House system itself was something primarly negative (rather, she showed its many benefits too). The epilogue merely shows the adults are now fully aware of those excesses and keen to warn the kids - that's a change of perspective.

Another theme included in the epilogue (and the final books) is that now evolve again normally. Voldermort wanted to establish is order which would endure forever. He's the one who wanted stagnation. Harry brought things back to normal. New kids are born, people grow older, teachers retire or die and new people follow in their footsteps.

I thought Rowling did well with the epilogue, and even returned a bit to the tone of book 1 for it, which was a good choice.

I don't really care much that it's in the movie or not, though. The movies have done away with much of Rowling's subtleties (from Harry's relationship to ghosts like Nick to getting rid of the scene with Neville's parents and so on and so on, and the depth of Harry's relationship with Sirius and how Harry sought a father figure in him and Sirius struggled not to see Harry as a friend/equal instead was downplayed in the movies) to focus on the trio and turn into the main story of a movie stuff that with Rowling were more plot devices around which to build her story (eg: the Triwizard tournament - the movie virtually kept only that of GoF) and the epilogue deals with things that have played a far more secondary role in the screen adaptation that they did in the books and were far more action-oriented when the books were more relationships-based, so the epilogue might well not be appropriate to the tone of the movie, which from the trailer will be damn epic (and that I wouldn't be surprised ends with a huge celebration at the school instead).