Considering that a game's financial success is mostly dependent on casual players, Skullgirls is quite a hard sell for the following reasons. BTW I love this game.
1. LabZero isn't a major company (aka Capcom, Namco, SNK, etc.), but rather an indie new company. Indie games are all the rage these days but that is mostly with other genres. With fighting games brand name seems to make a huge difference. Also that most fighting games are Japanese made will also hurt it.
2. Currently only 9 selectable characters. Especially considering this is mostly a team game, it's going to seem very small when compared to UMVC3, or SF4, KOFXIII, etc.
3. Apparent touch of death combos. These aren't true touch of deaths usually, but usually with resets can feel like it to new players. Seeing your health go from full to zero in one touch can be very frustrating, and it will be awhile before players can start to spot and defend against resets.
4. Mike Z constantly comparing the game to MVC2. This can give the illusion that it is an MVC2 clone, which it is not. However MVC2 still has a huge playerbase so people who think that, will just stick with MVC2.
5. All female cast. Many gamers avoid doujin games for this very reason, they feel the game is more about sexy fanservice than gameplay.
A few things that can be done to help promote the game...
1. Keep throwing out that the music composer is Michiru Yamane of Castlevania SOTN fame. Most fighting games nowadays aren't so great musicwise, so Skullgirls really stands out in this regard.
2. Point out how different all the characters are from each other, this should diminish peoples' concerns with cast size somewhat.
3. Point out that 4 more DLC characters are on their way (some of them male), and possibly more after that.
4. Point out how much of an impact fans have in influencing the game.
5. Promote that it uses the coveted GGPO online system, the closest u can get to offline without actually being offline.