No, you don't "have to" stand in front of the Castle to see the fireworks. As Robo said, if you want the full Disney experience, in front of the Castle is the place to be. However, having said that, we rarely go in front of the Castle anymore because we don't feel like dealing with the crowd. We go to one of two spots. Either toward Liberty Square, standing outside the Hall of Presidents (across the roadway from it). That's a pretty good view with low crowd levels. An even better view is right behind the Castle, near the carousel. I don't have the map to show it, but walk past the carousel, then go another 50' past the stroller parking...in the direction of BoG. That's a fantastic view with almost no crowd. You can still see the Castle right in front of you, it's just the backside of it. The major difference is that instead of all the fireworks happening right in front of you, it's 360 degrees around you. Some are in front of you, some are behind you, so you're having to turn your head a lot. But that in itself is a really fun experience to have them going off all around you.