A single tweet page is 2.0 MB
His rant doesn't seem too informed:  "aggressive anti-performance and apparent contempt for the web by Twitter’s designers"According to his charts most of Twitter's page is JS/CSS and presumably set to heavily cache.  Very little is data.  Once you've done the first page load Twitter's pages will load quite fast and efficiently.  While quite a lot of JS, this is good design, not bad.