Honestly, and please don't take offense...but one of the few countries that I have observed of people not taking kindly to people moving up a social class is England. And I say that as someone who loves all things England. From what I can see, the English tabloids (as does the American tabloids) love to have someone to kick around , and for some its the Middleton's.
From all the appearances it looks like the Middleton's have worked hard to provide their children with better than they have. Isn't that what all parents do....aspire to give their children a better life than they have. In this case better is a better education which puts them in a different social orbit. Don't we all socialize with people that we knew in school? Now if the Middletons are living off borrowed credit and haven't gotten any money, and people are stalking them for debts owed to them, than that would one thing. But I haven't heard anything like that. They make money, they pay their bills, etc.
And honestly, I think Uncle Gary's issues became famous because he was Kate's uncle. The press might have cared a little, and the police a lot but really the only reason a lot of us know about him is because he is Kate's uncle. Unfortunately, there are people like him in every country and their information is hardly splashed about the news.
I think iluvbertie pegged it right when he said benefit by association. Everyone associated with the royals gets a little more attention. Some because of their proximity to the throne, money and looks get a little more attention than most. We know about the Spencers because of their tangled history with the British monarchy and their dysfunction and because they are rich. We knew about Fergie's father because of his association with Charles, polo and his misdeeds. You don't know much about Tim or Sophie's family because they appear to be normal. Frankly, they appear boring and as we all know, boring doesn't sell magazines.