Yeah I agree. I'm not against the idea of the user staying on the same page to get more content, but for example when you click a tweet on the web to expand it

Yeah I agree. I'm not against the idea of the user staying on the same page to get more content, but for example when you click a tweet on the web to expand it and see replies, I would have designed e.g. a pane that 'slides in' from the right and can be closed by sliding out, rather than the frankly amateurish overlay. Also compare the way Facebook will let you 'expand in place' when you click see more/show replies/etc. rather than overlay their feed with a popup.