That is true, however, both Henry I and II did their best populate the Isles. I believe Henry I had about 20 illegitimate kids. (I actually hate that term). I would like to see how Plantagenet DNA was dispersed..
When they dug up the remains of what is now thought to be Richard III, I remember the archaeologists using the DNA of a Canadian carpenter with Plantagent ancestry as a validation. So there must still be a lot of Plantagent blood around!