Lincoln:
I would only comment on my own stories if someone has posted a comment which I think is either wrong (have had one or two of those) or offensive (none so far thank goodness). I try to respond to all by a personal message, but sometimes (eg in the latest contest) it is not always possible.
If authors don't want to respond to commenters individually but still want to acknowledge the comments they can always use the "author comment" facility to say something like ... 'Thanks to everyone who commented.' That's not really what it was intended for but can still be used in that way.