Heh, surprisingly, I actually prefer the name Rock Man, as opposed to Mega Man. I'm unsure why, to be honest. Meh, I also like Forte, over Bass.
Also, he's not named after a "Rock," as in a Sedimentary or Igneous sort of rock. It's Rock as in Rock and Roll, hence the pun of the Character's names... Rock and Roll. Erm, it seemed sort of obvious. If you hadn't noticed, most of the Character's Japanese names are related to music:
English Name - Japanese Name
Rock/Mega Man - Rock/Rock Man
Roll - Roll
Break Man/Proto Man - Blues
Bass - Forte
Treble - Treble** (?)
** - I'm unsure of its Japanese name.
Well, a lot of 'em anyways.