top 300 currently live is going to be pretty much all the channels with at least 35 viewers or more. Sure it sucks for the smaller streamers still building up but i dont know how exactly people are getting so angry....
just go down the list yourself at a given time of the top 300
http://www.twitch.tv/directory/all
start with the obvious League, Dota, starcraft minecraft but then saw dark souls, skyrim, runescape, megaman, mirrors edge, fighting games, kirby, dk64, yoshis island, papers please and all sorts of other more obscure games. scrolling past 300+ will be that 1% usability issue who knows maybe it because a performance and memory issue at that point.
As for US only i dont know maybe its due to advertising logistics.
meh but whatever, fuck microsoft right?