Pull-down-to-refresh was pioneered in Loren Brichter's Tweetie (now bought and remodelled as the recently not-so-great official Twitter iOS app).
This makes sense because Twitter lists its content in reverse chronological order, with the latest posts at the top. When you're scrolling towards the top of your stream (by dragging down) to check the latest posts, it's natural to continue the action and trigger the refresh.
This is not the case, to use the most obvious example, on a Facebook comment thread in the Facebook iOS app where the latest comments appear at the bottom. I scroll to the bottom to read the latest comment then have to scroll all the way to the top, and past the top, to trigger a refresh... which I then have to scroll all the way to the bottom to read. Why?
This can get pretty frustrating on long and relatively active comment threads and doesn't make any sense. It would be far more natural to just be able to scroll past the bottom of a comment thread and trigger the refresh that way.
The only possible defence for this is that Facebook also does legitimately use pull-down-to-refresh in their inbox and on the notifications list (where the items are newest first) and thought that it would be confusing to incorporate both methods in the same app. I don't buy that for a second though: I bet some users don't even realise you can pull-down-to-refresh on oldest-first areas of the app like comment threads - after all, it's pretty odd to scroll up past the top of the original post to do this at all.
Does anyone know of any apps that have newest last lists that do use pull-up-to-refresh?
Update: The latest version of the Facebook app has removed pull down to refresh from areas that update at the bottom of lists.