I see a glaring issue in many popular implementations of the modern web app -- not using hyperlinks for all actions.
Steam is definitely the worst offender I have experienced so far. If you have ever used their community portals via browser you will notice that you can rarely ever right click on an action and open it in a new tab. Google also does this in most of its apps as well. New tabbing actions is what I am all about. In fact, it's the main, if not only reason why I can honestly argue why web apps can be better than native apps. But no, instead of using hyperlinks for each actions, they use a generic html tag like a span or a div and then listen for click events on them, which is fine if you click, but when you right click the browser has no idea that it is actually linking to an specific url or action.