Van Buren wasn't exactly the backbone of FNV - they took some elements from it here and there, but the overarching story was mostly distinct. (The biggest thing they probably took was setting it in the southwest.)
Yes, Caesar's Legion and the NCR-BoS war (and, albeit through heavy changes, Joshua Graham) came from VB.
My statement was intended to convey that most of the underlying plot did not come from VB; just a number of particularly meaty bones, rather than the spine.
