This is no longer true with the HR20 and newer stuff (which you need to get most of the HD content on DirecTV). The channels are right next to each other, and it's possible to set it to automatically go to the HD channel if available.
To be honest, they are pretty much identical services with a few important differences.
DirecTV has better HD content and selection than Dish does, and will in the near future. If you're inclined to subscribe to Sunday Ticket (the NFL package), you can only get that and a few other fringe sports packages on DirecTV. Otherwise, they are very similar offerings.
Unfortunately, living in SW MO, you're only going to be able to pick up what's on the national broadcasts, and ESPN Full Court.
On another note, I usually get the College Gameplan package every year. It's alright, but there are usually only 2 or 3 games a year I watch on it that I couldn't have otherwise gotten. The Big 10 network, and having all of it's alternates available, really kicked a lot of interesting games off of gameplan. If you're a tremendous CFB junkie, it's worth it. Otherwise, I'd avoid it.