Was thinking about this and I'm not really sure where it comes from? Mega Man's from the 1987 yet he's based of Astro Boy, which was from 1952. Mega Man X was from 1993 and drew a lot from 1972's Casshern; the storyline, Sigma, Velgauder. Both retro as hell when they came out. Mega Man Legends was from 1997 and is, what, Evangelion and Yatterman? So I guess that one was current to what was on television at the time. Mega Man Battle Network came five years after Pokemon. Not retro, but it was hardly striking while the iron was hot.
Astroboy was this:
by the 80s he looked like this:
which was like the standard look of 80s anime:
and in that context Mega Man was born:
For Battle Network let's look at what was hot at the moment:
This is what I like to call the "Pokémon look":
it became almost the norm for kid-friendly looking games too:
Note that these games were released on the Gameboy Advance too.
And the "tron lines" that are kind of popular right now in American comic books and shows:
I mean, even Batman looked like this for a while:
Yes, I selected my examples carefully and avoided other versions of Mega Man for two reasons:
1. To avoid this post getting longer/busier that it already is, and
2. Because I think the different versions of Mega Man share some design philosophies with the examples I provided.