In pre internet days, genealogy was the realm of the landed and titled, because they had access to the documentation. Now that we have many great resources online and archives have become accessible, the average person can trace their ancestry much more easily. The strange thing is that more and more people are finding that,though they are mostly descended from humble people, that there is at least one landed line in their background, usually in the late middle ages. The landed class of England is descended from perhaps only 250-300 Norman families, so it is inevitable that, if you get a good line going, you will find more and more of these Anglo-Norman families in your background. Given the fluidity of English society in the late middle ages, you might even find a line that gradually becomes grander and grander till it reaches a royal line. This line may be an illegitimate one, or it may be a legitimised one (such as the Beauforts, children of John of Gaunt, 3rd son of Edward III and his mistress-afterwards wife- Katherine Swynford.) These lines are as valuable as any 'legitimate' line and take you back into the Plantagenets, who then descend directly from William the Conqueror. He is, of course, direct descendant of Rollo of Normandy.
The descent is there, almost certainly in the lines of everyone of British descent (as it has been calculated that we all have at least one descent from Edward I Plantagenet): the only problem is finding that line. It means following every female line and taking it as far as it goes, and looking online for those who might have already traced some of the ancestors in our lines.
I hit the jackpot in the early 2000s when I found out I had a gateway ancestress, Harriett Bromfield, who took us straight back to the Plantagenets on a number of lines and thus to the house of Normandy.