Markw,
I would have thought the obvious answer would be that FMD/BTV are notifiable diseases, with consequent movement restrictions etc. and PDNS/PMWS aren't. As DEFRA have shown that in an emergency they are unable to contact their vast databases of farmers direct, the only means they have had to notify farmers of movement restrictions has been through TV, Radio and the national press so they have sought, and received, maximum publicity.
Once in the media view, such things depend upon their dramatic possibilities to remain in the spotlight. With the vast scale and dramatic effects of the burning pyres etc from 2001 still fresh in the public mind, the FMD outbreak was inevitably very newsworthy. With the, from news impact point of view, low numbers of farms affected and animals culled in this outbreak it would have disappeared from high billing in national news except that it is a) very close to London and b) the result of a leak from a Government establishment c) happened in the traditionally quiet news month of August. Were it to have arisen from some other cause in Scotland, Wales or the further reaches of England in September with Northern Rock, Burma, Party Conferences etc to compete with, it would have received much less attention.
With there being no slaughter policy with BTV and it being up to individual farmers to deal with infected stock as they see fit, and with carcasses being disposed of through normal channels, I expect the disease will fade very much into the background of non-trade media.