All top10 have done is an order on the results in the speed test map and taken the bottom few results to talk about.
No one probably considered exchange location, did this result look odd compared to surrounding streets etc.
Our own maps show lots of oddities, e.g. people living on edge of an exchange area getting better speeds than those living one road away from exchange. The upstream speed sometimes suggests they are still on an old half meg product, and also you have no idea when its a handful of tests whether they were testing due to a known problem, e.g. on request of ISP.
As always though, bad news sells rather than the good news