how to build a joke

Do you think this is true?

I think many comedians does build a joke intentionally to be more prepared in what they are gonna say and how they are gonna say. 

Have you been aware of this notion before? 

I have not been aware of this before. I thought many comedians did not build they're joke intentionally.

In what way is Abbott & Costello's comedy an intentional act with a purpose?

In the beginning of the video when Abbott asks the audience about what they wanna hear from. Immediately there was a person that shouted baseball and he also gave Abbott and Costello the crops
I thought that was something they did with a purpose. And the whole " Who's on first " is written and  performed in many places by Abbott and Costello and I think this act is an intentional act with a purpose.

Are there other components of comedy mentioned by Martin that are present in "Who's on First?"

There are not a lots of comedy mentioned by martin that are in "Who's on first" but I would say there are some components of comedy.