Complete rubbish - several years ago the law was changed to stop this kind of practice. As long as the parts used by the people servicing the car is acceptable to Ford, which most of the major brands would be, then they cannot say that.
If you really want to be careful you could get your independant servicer to use genuine Ford parts . . .
But that's not what he said Paul - he said 'if you don't have it serviced (AT ALL)' the warranty will be invalidated - and that's true.