Dr. Hari.J has an interesting blog post on this subject. He quotes Swami Vivekananda who opined that Hindusim and Buddism cannot survive without each other. On the other hand, as Dr. HJ rightly mentiones, there are few places in the world where the two religions do exist independently, without the other.
Geographically yes, but perhaps they are not intellectually and philosophically independent. I suspect the Swami meant the latter. Indeed, Indic religious philosophies (Hinduism, Buddhism, Sikhism, Jainism) are all joined at the hip and generally thrived up until a few 500-odd years ago due to healthy competition (i.e., very vigorous discourse and debates. Presumably, changing 'religions' in India (one cannot be sure if they thought of it as a religion as defined today in the western world), during those days was perhaps as easy as the switch between windows, Linux or Mac. These debates had an impact on the ground reality and "optimized" the Indic religious philosophies better. For example, Adi Sankara of Kerala is credited with having "upgraded" Hindu philosophies that eventually allowed Hiduism to survive in India. This he did via vigorous debates with Buddhist leaders.
That process is dead now and perhaps the Swami implied that he did not want this process of discourse and debate to stop. Not surprisingly, a lot of the angst in the world today stems from frustration with entrenched harmful practices within ones own religion, in tandem with of a lack of mutual respect for how the other religion's core philosophies are the same and how they are different.
[Edited on 7/22/09 for typos]