I know a lot of guys swear by Steam to purchase and manage their game library. I use Steam as well, for everything except DCS.
Why?
a) Ease. When you purchase directly from ED, you don't have to jump through any hoops to transfer licenses, etc.
b) Compatibility. ED constantly warns of various incompatibility issues with modules purchased through Steam. While I believe they are all able to be resolved after a fashion, at some point, having purchased a module on Steam is going to lead to tears and sadness.
c) $. When you purchase through Steam, they take a cut. When you purchase directly from ED, ED gets all of your money. If you imagine that your flight sim dollars may support further development and improvement, it makes more sense for ED to get it than for Steam to get it.
