In the section of the book (same one) that I'm at, it's talking about the increase in the importance of titles and family. Again, it's in the section "Royal Blood and the Royal Brood."
It talks about how in the fourteenth and early fifteenth centuries, the idea of royal blood had become very important. Titles were being invented, and given to members of the royal family, to show who they were and who they were related too, more importantly. For example, Edward I created a title still used today by naming his eldest surviving son and heir to the throne, the Prince of Wales. Prince Charles, son of Elizabeth, carries that title today. It's fascinating to read about titles being created that are still in use today.
Other such titles were given to anyone with "blood royal" to separate them from the the general public. It wasn't enough to just be a noble. You also needed some royal blood to receive more validation. In fact, three of the six noblemen given the title of "marquess" were related to the king. Also at this point, members of the royal family wanted to describe themselves as the "uncle/nephew/anything" to the king. They did anything to prove that they were closely related to the king. Names held power in this society, and to associate yourself as being close the king, then you had power, no matter how big or small.
The time period of this is also important. At this time, the Lancasters and Yorks both had claims to the crown, and wanted to do anything to strengthen that claim. Illegitimates and half siblings were used to add power to numbers, while before they weren't really considered. Both would want to exaggerate their connection to the crown and prove their validation in getting the throne. The Tudors were also big on titles, though I don't have enough solid information yet to really understand their importance in it.
From my reading, it is also clear that the English wanted to build up a royal reputation greater than the French monarchy. England and France have always had an interesting relationship, and the importance in being part of the English monarchy, and giving out important sounding titles would have served as a sign that the English really wanted to surpass the French in reputation.
The topic of blood royal will serve as an important part of any prospective thesis i have. It shows how being related to the king, or a part of the royal family was important, and I want to go deep into the reasons of why this was. Sure, it's cool to be the brother of one king and uncle to that king's son, but what's the importance behind that? Is it for the title? The power? Or did they just get a front row seat in the all the drama surrounding a monarchy? I guess I'll have to read more to find out.
Since I'm moving into Lancaster and York, here's a complex look at their family tree. From what I understand of it, it looks as though Henry VII (Tudor, descended from Lancasters) married Elizabeth of York, so their son, Henry VIII would have had Lancastrian and York blood, giving both families what they wanted. Cool, huh?