I'm not disagreeing with you, but I'd just like to say that that is hardly unusual in the slightest, particularly in children's/young adult literature. Also, keep in mind her British nationality. In the US, wealth is more likely than not earned (at least by some recent generation). Throughout much of British history, the wealthy were the snobbish nobility who operated with little care for their underlings. It's important to note, that the "rich" in Harry Potter are not only rich. They are people along the lines of what passes for wizard nobility, or at least of that heritage. The Malfoys are an excellent case. I'm sure that some Brit will correct me on this, but I have not really ever seen any British music or literature glorifying the rich and noble.

I also observe that Rowling did juxtapose this bias. After all, Voldemort, the Big Bad, was just as bad off as Harry, if not more so, when he came to Hogwarts...the difference was how he overcame it.