“You like what you’re used to.” That's what bed-ridden Lord Grantham said to a mischievous, truth-telling, little boy who uninvited wandered into his bedroom for a jolly conversation. This unexpected intrusion was possible because the house had been opened up to paying visitors for the day to raise money for the local hospital. (We seem fated to hear about that hospital and the ridiculous quarrel about its governance every episode , no matter how uninteresting it is!) Of course, we are now so used to great houses (even Buckingham Palace) being opened to visitors that we may find it hard to appreciate what a challenge it was for the family, which was clearly divided on the issue. Of course, Carson and Molesley grasped the potentially revolutionary threat this lifting the veil on the magic might mean for the old order. The rest of the family just had trouble grasping what people would want to see. This was meant to be funny - aristocrats so incurably out of touch that they don't understand how strange (and therefore interesting) their way of life is. Hence the stereotypical "out of the mouth of babes" conversation in His Lordship's bedroom.
That the aristocrats think they are just leading ordinary lives in an ordinary home may reflect how out of touch they are. That they don't know much about the building or its art (painfully demonstrated when they try to act as tour guides) show how "at home" they are in their surroundings, which for them seem to lack the historical, artistic, and other significance the public inevitably invests in them. But the fact is that ordinary people, while they may envy the privileges of the old aristocracy, don't necessarily envy the life itself. Hence the intruder's honest question: surely you have enough money to live more comfortably, so why don't you live in a more comfortable house?
In that question - and Lord Grantham's slightly muddled answer - is revealed the great chasm between the new thinking (or, rather, feeling) of the 20th century and traditional thinking. In the brave new world we are being dragged into with each successive episode, it's all going to be about how we feel and what we want. And in that world there will be less and less room for the old-fashioned pieties the old order at least purported to represent.