Because those comments made me realise that what I originally wrote was (1) not quite right and (2) not perfectly clear. The extra paragraph I added, so far as I can tell, makes just as much sense if you haven't read those comments; I just wanted to acknowledge that it was other people's comments that led me to add it.

Given the choice between a discussion where some bits have been clarified in the light of later comments, and a discussion where some bits are needlessly confusing or wrong, I choose the former.

(I might take a different view if there had been lots of replies, which might have been invalidated as as result of the edit. But there weren't; just those two.)