you fool. X started on the SNES. all games that were being made by capcom at the time (both classic and X) had followed the plans of the bigwigs at capcom headquarters. the abandonment of cartridge based games. While capcom were continually dishing out games for the classic generation on the NES, they branched to the SNES in the form of Mega Man X. Capcom's money conserving ways, much like square soft's ways, were to switch over to CD based format.
Mega Man 8 & Mega Man X4 started off on the much cheaper format of the 5th Generation of consoles. the only series to be completely Nintendo, would have to be Mega Man Zero, Battle Network, Mega Man ZX, and Star Force. cough.
None of the Mega Men affiliate with Nintendo, do matter how you spin it. it's all visual and a personal preference butts into ones debate if it suits them (myself included). In all actuality, Zero (MMZ version) fits in the most, but we don't want the blue bomber to be replaced by zero again, now do we?