Hi Ryan. I think the only answer to this one is “why not!”. There are things in the solar system out past the planets even. The planets formed from matter in the solar system clumping together. Because a lot of the matter ends up in the sun itself, and just from the physics of the whole thing spinning around, planets close in to the sun tend to be small, and ones further out tend to be big. Once you get out further than that, things get smaller again, so they don’t get called planets.
During that process, lighter elements that weren’t getting incorporated into the proto-star (our Sun very early on) at the center of the disk migrated outward. These are things like hydrogen, helium, and even water. This is process is called differentiation. These lighter elements tend to collect to form more massive bodies so the big planets form further out, with little rocky planets like Earth being much closer into the Sun. That’s why some planets are farther away from the Sun. The process wasn’t quite complete with just that though. There is something called “planetary migration” (oooo! another buzz word!). Planets actually may rearrange themselves after formation to make the entire system more gravitationally stable. So some of the planets are in their current spots because of this process (check out more info on wikipedia here: http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#Planetary_migration)
So, yes! There is a reason, and it has everything to do with the dynamics of planetary formation!! We have even looked at other star systems now with known planets and seen that planets can be quite far from their host stars!!