why are urban regions contiguous

It's very unfortunate but it sometimes feel the academic world remains ages behind. At a conference last week, I was struck by Sir Peter Hall's "functional urban regions" (FURs). Although Castell's 'space of flows', Saksien's 'global cities' and Taylors' 'world city network' had its share of attention during his speech, these theories are not included in evaluating FURs. Why are FURs contiguous ? Aren't there as many commuters between London and Brussels as London and the South East ? How about NY-LON ? The answer appears rather simple and disapointing : lack of data on air / rail flows, hence on long distance business commuting. It's time academics nd the transport industry share knowledge so we can truly be in a space of flows.