I really don't think the Magic Missile change was a very appropriate use of errata. They didn't change it to fix a mechanical problem or a balance issue, they just changed it to make it different, it's not like the printed version made it into the book by mistake or something, and it's been like two years since 4e came out, such a bizarre change to make after all this time. It's gotten to the point where the original books are practically useless as reference if you want to play the game in its current incarnation.