The advertising is - as is all advertising - about perception.
The notion that referring to something as 'Yorkshire' implants the notion of 'no nonsense, straightforward, no tricks, honest ...' and so on, which will appeal to the demographic required to take in the message.
It follows the same principle as the PlusNet catch phrase - 'We'll do you proud ...' with exactly the same intention - imply honesty and no-frills to catch your demographic.