The packages are very skillfully crafted. Each package is designed to give you a reason to consider upgrading to the next tier. It's all about the up-sell. Anyone who has ever tried to pick the right package to get all of the channels that they want in the lowest tier knows exactly what I'm talking about. Unless you want to go all the way to the top, there is always a trade off between cost and specific channels that will force you to think really hard about how much specific channels are worth to you.
Earlier this year, my wife and I actually did an audit of which channels we actually watch regularly, created a matrix of which packages included which channels, and then had to decide what we could live without.
How exactly they decide, well, I suppose that is their "secret sauce". All I can say is that DISH is an expert at it.
-SF