I don't see keyboard navigation as being standard, and what seems to be standard isn't very good. Perhaps browsers should have an option to limit JavaScript's ability to override keystrokes used in navigation. I use Pentadactyl, a vi-like keyboard navigation plugin for Firefox, which doesn't seem to be plagued by this problem. I learned about it here on HN.
In a menu, all I have to do is read to find out what the keys are for each command. Much like each browser has a Back button, it'd be nice if all browsers could agree to provide a "legend" displaying the keystrokes that a web site has defined.
Of course, once the browser can display the mappings it can offer a more sophisticated way to disable them. For example, checkboxes for each key so you can keep the ones you like but get rid of the stupid ones.