Do you want an explanation here?
For Airman: "cf. R20 & MM2 (NES) manual"
In R20 Rockman & Rockman X Official Complete Works (Japanese version of course) it's Airman (in Japanese signs and AIRMAN as transcription) and in the manual of Mega Man 2 (NES) it's Airman, AirMan and Air Man (sorted from mostly used to less used), thus more often Airman is used (or should be used; as it might be miscounted). Similar with other Enemymans.
For Megaman Battle Network, just in case: e.g. cf. Megaman Network Transmission (PAL) game backcover, similar with Megaman Zero games (PAL).
For Megaman and Megaman X:
Game logo might be more likely be "Mega_Man" (_=linebreak) thus "Mega Man", but the guy's name inside the game at least in the older Games should be more commonly "Megaman" (secondary sources e.g. Mega Man 4 Script & Mega Man 2 Script - though it's not those secondary sources who decide about right/wrong as they might be wrong, but one can see "Megaman" resp. "MEGAMAN" or so inside the games). -Shao Pai Long (talk) 22:44, December 12, 2012 (UTC)
Read the link, it explains why I'm undoing your edits. Most Japanese sources write the names together, while most English sources write with a space (Air Man examples: Mega Man & Bass database and Archie Comics)
If the names were to be written as they appear, there would be many names with spaces and others without.
"while most English sources write" - is there any proof for that? I doubt it.
Also: English =/= English; e.g. difference between US-America (USA; which imho commonly is retarded anyway as proven by date system, length system and temperature system) and European PAL; dunno about Australia though.