Quote - First you wrote:
"So the main reason for Poser users being "upset" is the loss of a content provider and the market force it uses to drive other.."

Then you wrote:
"For most Poser users DAZ is still exclusively a content provider. That is the present situation, not only the past."

and then:
"V4 content is still being sold at the DAZ store. How long? As long as it sells"

Accepting the two latter quotes as true
 So why are there some users "upset" then""

There will be LESS content because some will be Genesis only. This means LESS choice

Quote -
well I refer you to the blunt wisdom of "Imackenzie"
who recently wrote: ( paraphrasing)

"The masses dont give a rats patooie about weight Mapping & SSS they just want the latest Vickie"

This and similar threads have proven him to be correct

When did I say the masses did care about it? I care, but most don't.

They will however still complain/be upset because some of the new goodies (textures, morphs, pose sets, clothes) they want to have will not be usable.