Charcoal, I think you are failing to see something major in your argument. You are claiming that FFVII was a really really good stand alone game. I agree with you. Though I haven't taken the time to figure everything out myself, I have figured out quite a bit, based on the original game alone. And I do believe that it is entirely possible to discover everything there is about the original game just by playing the original game. However, this does not mean that the story is complete. It just means that the first chapter was told really well. Now, in Advent Children, the major story point (despite what it may seem) was Cloud finally releasing his guilt about Aerith's and Zach's deaths.

If you want to rely only on the original game, Cloud never released this guilt. However, in AC, Cloud did. Obviously, if this is part of the story, FFVII does not complete the story. Because AC came along and helped us understand more about it. Two years after Meteorfall, Cloud released his guilt. There is no mention or even a slight reference to this in the original game. Do you know why? Because the game only deals with what happens in the game. It doesn't deal with what happened two years after the game.

Thus, AC was needed to complete the story. And that's not all. Not only did Dirge of Cerberus add onto the original storyline, but it also gave us quite a bit of background on Vincent's life. There is no conceivable way to figure out all of Vincent's past just by playing FFVII. FFVII tells us that he was a Turk, that he loved Lucrecia Crescent (the original game actually never even gave us her last name), and that he had some dealings with Hojo because he never tried to stop Lucrecia and Hojo from completing the Jenova Project by injecting their own son with Jenova cells.

Never does it tell us anything else about Vincent. However, for all you know, Square Enix could have written out Vincent's entire history before FFVII was even made, and then released it in a new game which not only gave us this information, but also new information. You want to know why Deepground is never even mentioned in VII? Because it was a completely secret organization. Reeve didn't even know of it's existence, and he was in the President's top circle. Only President Shinra (not Rufus), Heidegger, and Scarlet would have known, according to Reeve, as stated in DoC.

So, as much as FFVII is a very well told story, it is hardly complete. Only paying attention to the original game and not the Compilation would be like reading the Hobbit and choosing to believe that the Lord of the Rings is an alternate story that you can choose to believe happened or not. Sorry, doesn't work that way. The Hobbit and LOTR are a package. Whether you like it or not, both things happened in the same universe. Same with the Compilation of Final Fantasy VII. Deal with it.

Edit: By the way, Elly, would you mind if I quoted that bit about how there are three sides to every story, yours, mine, and the truth thing in my signature. I think that is an absolutely fantastic quote.