It seems that derailleur is synonymous with bicycle, but it doesn’t have to be. (If you’re one of Sheldon’s acolytes, the derailer.)
Internally geared bicycle hubs have been around for a long time, with a proven track record of quality. We’re not against the derailleur, we’re just awfully fond of the internal-gear hub. They’re more reliable and require less maintenance. That’s a theme with us–making decisions that make it easier for you to hop on your ride. Speaking of which, internal-gear hubs can shift while you’re stopped, and that’s pretty cool in the city or if your mind wanders looking at, say, the awesome mountain scenery around you.