I didn't know that... I must say the balance would have been off a bit if Dedede and Mewtwo had been in SSB
64 - series-wise, I mean. Marth would have been 'just another Link', probably... but
Bowser? Yeah, that could have been very cool. I was quite surprised that he didn't get in there, actually. It would have been a good way to keep DK from being the undisputed powerhouse (if Falcon wasn't enough, that is), but I must say I liked that nothing could match Donkey Kong's lethal wind-up punch. That thing was killer as a well-timed jump attack.
I like the way the developers managed to weave more and more retro references into each SSB game. Brawl's DKC series tributes are what makes it almost tied for first place in this poll, for me. So DK's final smash was a bit of a kick in the pants, but oh well. You can't win 'em all...