Two questions that touch on common considerations of "Englishness" and its conquests.
I'm not a UK citizen, so my understanding of what is commonly considered the start of the English Monarchy might be wrong. But in the English histories I read/watch, people generally talk about the Norman Conquest as the real/most significant beginning of the English monarchy. Why? There were Anglo-Saxon monarchs before, and part of William the Conquerors claim to the throne was his relation to the dead King. It can't be because it was the most recent foreignly invaded Monarch, because Henry Tudor did that. So why does the history of the monarchy so often base itself around the Norman conquest?
On a related note, why do we consider the British to be "Anglo-Saxons"? Why not Britons or Celts? Or even Romans? Or Normans? Was it because the Anglo-Saxons brought the first unified culture? Since, to my understanding, the Britons and Celts didn't operate nationally but more in clans? Was it because the Anglo-Saxon invaders intermixed with the local population more than the Normans? Did many Normans even come over in the conquest or was is mostly just a Norman ruler ruling over an Anglo-Saxon people?
Ok, a few things to clear up:
So in summary- England only became stable after the Norman conquest and many of the great royal buildings were started then- hence the importance of 1066 in England's national identity and to the Monarchy
On your later question-