On #1: They might remove Hangouts from Gmail-on-Chrome if they planned to integrate them directly into Chrome/ChromiumOS. More likely, though, is that that button in the top-right corner isn't a drop-down, but rather represents a currently-collapsed Hangouts sidebar. That sidebar is probably expanded by default, like Facebook's.
On #2: it's well known that people have a bad experience reading extremely long (i.e. more than ~65em) lines of text. It's actually better to wrap a subject line onto several lines than to let it go on all the way across your 2560px screen. Ideally, web pages could just specify a maximum width you could stretch the browser out to. But, since they can't, they drop in some useless whitespace.