I agree with CA here.
Yes, browser writers should all use a common DOM but they don't, and probably never will so it's upto the site designer to make sure they do not lose visitors because the site does not work as intended on the browser the visitor happens to prefer.
There are problems with most browsers, and some mods for phpBB which do not work with some browsers i.e. the Advanced Quick Reply does not work in most mozilla browsers or safari, but it is fixable.. however Opera is another problem as it supports 'document.getSelection()' but it does not give the desired result. And spending time solving a problem that was not mine in the first place is not a high priority, after all real life has a use to.