My take

(on the 2 versions of the Intro)

Version B (which is also the real one :) is the better one.  It allows all readers--even those skimming--to easily locate key ideas of interest.  These are presented in the first sentence of each paragraph.  The rest of the paragraph then develops these ideas.  Thus, ideas are organized and details structured to be relevant to readers.

Here are a few details on the good things about Version B:

• Paragraph 1 takes us right to the contribution of this paper to the literature.  We are immediately told how this paper adds something meaningful to the existing literature.  
• The structure of version B is designed to suit its target readers' interests.  This is evident from the get go, even if you compare the first four words of each version ("The EITC is a" vs. "A widely accepted view").  Version B knows its audience and what is most relevant to readers.  Version A seems to misunderstand what is interesting to readers of an economics paper.
• The jargon used in Version B (intensive/extensive margin) is simply explained in a few words that everyone can understand.  Thus, no readers are shut out of the paper at the outset.
• Paragraph 2 boils down the essence of the research design to  a simple sentence that everyone--even non-experts--can grasp. The first  sentence promises to readers that the research design is based on a simple idea; the second part of that sentence fulfills that promise.

Now here is what is bad about Version A, in my view: