There are at least 2 core reasons why the nickname "Blue Bomber" is inappropriate for Megaman. Firstly, he does not have the inherent ability to bomb. He can obtain the ability to bomb from a few Robot Masters, but that is no more definitive than his ability to obtain fire based weapons from Robot Masters. Shall we call him the "Blue... Burner?"
Secondly, bombing things is not his defining characteristic. Besides running and jumping, Megaman's definitive characteristic is that he blasts things with his Mega-Buster. If he were nicknamed appropriately, he would be called the "Blue Buster," or maybe the "Blue Blaster."
Calling Megman the "Blue Bomber" is no less offensive than the bastardization of cover art and/or character names. "We butchered the localization, why not give him an inappropriate nickname, too?"
|Capcom themselves had officially adopted the nickname by the release of Megaman 8, 1997.|
But don't try and blame this on Capcom. Oh, no. Blame yourselves, fans. Blame yourselves for propagating this perversity for the past 20 years. Shame on you.