The original page mentioned in the ticket no longer exists, however http://www.weblogs.com/api.html and https://developer.twingly.com/resources/rpc-ping/ agree's with the original ticket, while http://blo.gs/ping-example.php & others disagree's (and agrees with core).
It'd be really nice if I could find a extendedPing spec that isn't hosted itself by a weblogupdates provider.. or at least one that the others referred to.
It seems that WordPress has simply always done this wrong, not sure for what reason, for reference r2572 was when the current code was added.
It also seems commonly accepted that most servers simply ignore the extra parameters, or handle a RSS feed perfectly okay, which also makes sense as the RSS feed should have updated at the same time as the post/page itself.