Interesting point. Do you really read twitter, or news feeds, from bottom to top?

Bottom to top makes sense for news feeds, ie. links to unrelated articles, where you want to see the most recent stuff first (and read these from to to bottom).

Twitter on the other hand puts top-to-bottom conversations in the middle of a bottom-to-top feed, which makes sense in gmail but just feels random in twitter — or maybe it’s just that the rest of my feed is random.