Puzzling over twitter app tweet preferencing

Why do the Twitterific, Twitter for Mac and Twitter for iPhone apps preference against tweets in the recent past? For example, if I want to catch up with what’s happened overnight – the US day – the feed has a gap in it jumping from, say, 3 hours ago to 16 hours ago. The Twitter for iPhone app lets you load more into the gap, but it’s not ideal.

It’s not as if I want to necessarily read all of those tweets, I’m quite happy to fish what I want out of the passing river of news, and let the rest go. And it’s not that I’m not comfortable with the philosophy that if something important has happened the river will deliver it a number of times over. What I don’t understand is why the apps choose not to just let the river flow past me. What possible reason is there to preference tweets from 16 hours or a few days ago over what happened in the last 10 hours?