Marth does do a lot of dash dancing, but what about wavedashing?
In this video of M2K vs. Armada, he clearly wavedashes ~30 times
This match was under 6 minutes, showing that he, on average, wavedashed at least once every 12 seconds
THIS match
http://www.youtube.com/watch?v=nJLDGiwUEsc&fmt=18 , which lasted under 3 minutes, had 31 wavedashes! Amounting to more than 1 wavedash every 6 seconds
And claiming that samus does not wavedash much is a gigantic understatement
Looking at this video of a samus,
http://www.youtube.com/watch?v=FrwF-K8yNg0 , it is clear that wavedashing (and wavelanding) is a core component of Melee. Amounting to 52 wavedashes (and wavelands) in under 4 minutes, he wavedashes on average once every less than 5 seconds. How can this not be considered a core component of Melee?
In your video
http://www.youtube.com/watch?v=-jczyAs7mU0&feature=player_embedded
You said "Sure, melee fox, falco,and falcon take a lot of speed to play at a high level, but they are the extreme examples. Outside of this group, the speed of input drops precipitously"
First, let's take a look at which characters "dominate" the competitive (tournament) scene
This compilation of data,
http://www.smashboards.com/showthread.php?t=267771 , ranks the characters according to their placement in tournaments. It awards points based on how the characters perform (10 for 1st, 7 for second, etc.), and larger tournaments are weighted with more points (see thread for explanation). It is CLEAR that Fox, falco, and falcon, DO dominate this, but jigglypuff, sheik, marth, and peach are all up there too!
Now let us examine the "precipitous drop" in speed input by taking a look at a thread that measures actions per minute of various characters.
http://www.smashboards.com/showthread.php?t=234508
Isai's falcon has 185 APM
DaShizWiz's falco has 228 APM
Darkrain's falcon has 214 APM
Zhu's fox has 244 APM
NOW...
Pink Shinobi's Peach has 214 APM
Mew2King's marth has 178 APM
Mango's jigglypuff has 225 APM
Kira's Sheik has 193 APM
Vans's Peach has 270 APM
Even Aftermath's Samus has 214 APM!!!
So where exactly is this "precipitous drop" in dexterity?
And then in your video you comment about "button mashing" such as Pit's Angel ring attack or pikachu's neutral a...What's this trying to point out? This is the exact same in melee. Actually, it's much more! In brawl, merely holding the A button with a character with a jab that continues into an infinite will keep repeating this attack (try holding the A button when using fox in brawl). Furthermore, once you press a for the first hits of the attack, you just have to hold a to continue the infinite. In melee, one must keep pressing the button at a rapid rate. And meta knight's whirlwind attack is very comparable to mario, doctor mario, and luigi's down B, where mashing the button rapidly results in the character rising and increases it usefulness...they're practically the same move.
You bring up sonic's ability to interrupt his attacks as well...however, this is present throughout melee as well. Canceling the second jump with some characters (mewtwo, ness, etc) as well as utilizing peach's floating ability or shine canceling is quite similar
And talking about the dexterity needed to glide toss and such is much less than that needed to, for example, double shine with fox, scar jump perfectly, shine bair at high percents with falco, or even nairing as fast as possible (
http://www.youtube.com/watch?v=bukOejeiUpw ,
http://www.youtube.com/watch?v=cCZIXfxSObw&feature=related )
So seeing all of these comparisons of "dexterity," how can one say that they are the same?