Nono, MSLN is not so much about the moe, but the shounen
GAR it has. Takamachi Nanoha was in SaiGAR after all. Trying to use moe as a reason to explain its popularity is pointless. Its likeability has more to do with its shounen elements. Just look at the Naruto, Bleach and One Piece forums. The only difference is in the gender of the title characters.
With nicknames like White Devil, Blazing General and Scarlet Iron Knight; we're not exactly talking about "cute-type" moe here.
It is about the Trinity of shounen. GUTS, COURAGE, and PASSION.
Cheers.