First of all, remember that this is a Hogwarts based rule. There is no ministry provision that all muggleborn wizards have to have a Hogwarts representative show up at their house, it is simply helpful. Just imagine if (prior to the books existing), you had gotten a letter telling you that you had been accepted to a magic school, Turkey Liver. You would throw that letter in the trash as spam.
Moreover, it is helpful to have a proper wizard show up to explain important laws, like the statute of secrecy. Not to mention being able to prove that magic is real. They could do a quick bit of magic to prove that magic is completely real, which would encourage the parents to accept the offer, and let their kids go to Hogwarts.
So, since this is completely up to the Headmaster's discretion, that means that <PERSON> gets to call the shots on who gets a proper visit. He knows for absolute fact that the <PERSON> know about magic. 821
<PERSON> had a witch for a sister and even asked <PERSON> to allow her to go to Hogwarts. So, she, at least, knows Hogwarts exists and knows what it is. <PERSON> may have been naive enough to believe she would simply let <PERSON> go to school, but I don't believe that is the whole story.
Remember the beginning of the Half-Blood Prince, <PERSON> knows what kind of people they are, and teases them by use of magic, (the bouncing mead). <PERSON> wanted to pay them back for the abuse they gave <PERSON>. It is altogether possible that <PERSON> knew <PERSON> would never receive the letters and used them to mess with the <PERSON>. After all, it is not exactly common courtesy to fill someone's whole house with letters, having the letters pour in through every euroffice of the house. Nor is it nice to chase the <PERSON> half-way across Britain, having every hotel stocked with three or four letters. Given <PERSON>'s nature, I assume he is having a private laugh, at the <PERSON> expense, and I assume he always intended for <PERSON> to give <PERSON> his first tour of the magical world. 573