I live in Rwanda and like a sizeable portion of Twitter's userbase, have very slow internet. When Twitter switched to their new design it got a lot harder to open their site... I kept using the old version until they removed it. I don't understand why - it's not pulling down a lot of data, it's not even making that many requests (~50), but this site and other AJAX rich sites just don't seem to work as well as the old less-AJAXy versions on a really slow internet connection with a bit of packet loss
You could argue that Twitter is more responsive than it would be using server-generated HTML pages. But the initial app download is much bigger than it would be with that method.
You can also play user-agent games to get the Android version in your browser. I prefer the regular mobile edition, but it's interesting to poke around; I've found three separate versions of the site just by faking out my user agent.