Yeah I think it's a huge problem that javascript/the DOM allow a page to have shortcuts and control over page navigation. This is so wrong IMO; the user agent should be in control. Because I am in control of my user agent.
Then it gets really hard to implement your own text box, if you cannot catch things like Backspace, etc. I think those things are relics because the web evolved rather haphazardly from a document display environment to an application development environment.
That "evolution" should not have happened. Maybe there's no sense in lamenting it now, except I think it's worth recognizing that we're still very much in need of both a reasonable web-like document display environment and a reasonable cross-platform untrusted-application-sandbox-VM environment.
As for implementing your own textbox that catches backspace, that's a great example of the type of thing that web pages should not be doing. User agents should be responsible for the existence of text-entry fields, that way they can serve the text-entry needs of the user. Different users construct text differently. Also the consistency of UI of allowing users to know how a textbox works (because it's not redefined for each site) is a UI achievement that we have now lost.
