Come on guys... it makes sense really.
Heathrow Director has little room for error. ATC in Europe might be quick to spot an incorrect type when taxying out when compared to the FPL. However at some of the more 'colourful' airfields in the less developed world, many ATCOs won't care if the FPL says B752 and a B763 is what he/she is seeing of the tower.
In some parts of the world, ATCOs have a very poor knowledge of different aircraft types and associated aircraft performance when compared to Europe and especially the UK.
Why should the Heathrow Director trust the ATCO on 'Bongo Bongo' tower to ensure that the FPL has been correctly filed with the correct aircraft type prior to departure?