That's probably it. Not as much space I think, but life support for an extended period of time. This is one key difference between Dragon/CST-100 and Orion: the latter is designed for extended deep space travel with full crew, and can support them accordingly, while the former are primarily LEO taxis with more limited deep space capabilities.

The problem with the Orion is that there simply aren't many useful missions. Orion can also go around the moon, just like Dragon 2, but for both craft that is the end of the line (at least for Crewed versions).

The difference is that Orion cost about as much as Dragon 1, Dragon 2, Falcon and Falcon Heavy combined. If we add the cost of a SLS launch it goes into another dimension of cost.