Yes, if someone writes something to which I have no substantive response (i.e. something non-trivial), and if their point is generally a good point, I simply upvote it and move on. The issue has been aired, adequate coverage has been given to various views; there is no need for the thread to continue indefinetely. It is only when I have a good counter-argument (which nobody else has already delivered) that I reply. (Or, sometimes, when a question is obviously directed at me personally.)