The first punch-out was a very casual game that ANYONE could enjoy.
I'm going to have to disagree with you on that one. Then again, I suppose I'm talking semantics as labeling any game as "for everyone" is a bit of a misnomer as I don't believe there to be any game in existence which absolutely every person on the face of the planet would enjoy. Case in point: me. I don't like Punch-Out!!, the game is just too difficult. I'm not even going to tell you how many times I attempted to beat the first round of boxers, as even with being as open as I am about my dearth of gaming skill, it's still too embarrassing to mention. 
Back in the day the game WAS for everyone, regardless of skills. I remember my mother, my older sister and my cousin getting into the game and being overjoyed by having beaten the toughest opponent.
The game comes from a very different time. Back then games were simple in execution and concepts, and thus were very easy to get into. But they weren't easy. The game got harder as you progressed and conquered each stage. The challenge came from the fact that as you got better the game kept testing your skill, but it was still a breeze to understand.
Nowadays, games are too complicated from the get go. They have to insert tutorials just to make sense of the controls and the game becomes more about trying to master the concept than it is about playing it.
This is why the Wii is such a hit with everybody. Its deceptively simple but the challenge ramps up as soon as you decide to master it. Wii Sports, in particular, is easy enough that you can skip the tutorial and still play it. But if you decide to go towards Pro status in all events it quickly becomes difficult, especially in baseball and boxing.
Punch-Out Wii will likely follow this philosophy. Start the game insanely easy, but then the difficulty ramps up as you conquer each fighter.