Ah, it continues. A long standing discussion equivalent to the following code:
Do While x<>y
x = 1
y = 0
Glen and David are both smart guys. Why can't they just get along?
I think it comes down to a sort of pride. David is quite proud of what he has done in promoting an "Agile Software Development" point of view. It is a pride both based on effectiveness and on novelty, that is it is the "creation" of something new. As such, there is a reluctance to acknowlege that it is similar or based on any past model. This is not unusual. Indeed it is quite common. "New" is the new "new". Humans are drawn to the new thing and there is excitement about adopting it. This is the ideal situation for selling something whether it is ideas, books or software development tools.
On the other hand Glen is proud too. He has pride in doing his job well and being part of a tradition of people who have done so. When someone slights that tradition (one which is actually rich with the adoption of the new) then it requires correction, and thus is born controversy.
I'd be remiss if I didn't take sides on this. After many years of architectural education it becomes obvious that "New" just doesn't matter all that much in the long haul. A lot of what is new is reworking of the old. And what matters is how effective you are at creating something that is needed or desired.
Just as an ancient statue of Medusa becomes just another block in the drinking water system for Istanbul, the ideas of the past are just building material for the ideas of the future. Failure to look at them and understand how they can be useful is wasteful. Failure to acknowlege that you have build upon the head of the Medusa is vain.
Note: When Justinian constructed the Basilica Cistern in 532 AD, bits of more ancient monuments were put to use. The current use is as a tourist attraction. Visiting the cistern is a cool and refreshing activity on a warm Turkish afternoon