The Falcon doesn't have to use a large diameter core because it uses a fuel and oxidizer combination that is three times denser than LH2/LOX.
That isn't a plus for BEO, or depots actually. I want a wider core for its own sake in that is is less cramped. One of the reasons Webb is so complecated is due to Falcon/D-IV H shrouds. ATLAST is a much simpler architecture. And its visible light too, where Webb really isn't, but that's another fight. http://en.wikipedia.org/wiki/ATLAST
It's called bloat and technological stagnation. Some people cheer it on.
I don't call tried and true stagnation. Rather, its things like Venture Star that try too much that should worry us.
Now (towards the last) this book actually calls for both HLLVs (BEO station construction, etc.) and RLVs (frequent flights, crew exchange):
The thing about depots is that leaking fluids can cause quite a mess: