Capcom made the decision to bring Street Fighter X Megaman solely to PCs initially so that they could test the download count -- but despite the fact that they still could have tested it for Mac based systems, they never represented the platform.
As of yesterday however, a fan has brought it upon himself to port the game over to the Mac. The unofficial port is based on the 2.0 version of the game, which has all of the bells and whistles like passwords and the like. There are a few bugs (switch to windowed mode for better output), but it's a good start.
SFXMM v2 for Mac Port [/rMegaMan]