To answer Stevie Wonder...'s question, I think that that moment was a "turning point" in their relationship because it was another instance in which Stevens cut off Miss Kenton emotionally. I thought that it was simply another missed opportunity for Stevens to show his feelings for her.
I have to say, however, that overall I found the book a bit boring.
The ending was sad, however, and I didn't think the reason for that was so much because of Stevens' regrets. I found it sad becuase, in a matter of five days of self-reflection and reflection on Lord Darlington's dignity, Stevens realized that his whole life had been basically a sham. Because Stevens was so dedicated to his profession, the validity and importance of which is now questioned, it appears as though he had lived for nothing.
It was also a bit depressing that Stevens clearly misinterpreted Miss Kenton's slight unhappiness as a sign that she wished to come back to Darlington Hall, and possibly to be with him; this was simply wishful thinking on his part. It didn't really surprise me, however. Also, when he discussed Miss Kenton were the only times Stevens showed any sort of emotion; when she told him she had no intention of coming back to work, he confessed deep pain to the reader for the first time in the novel.