So is this show actually popular with its target demographic, or is it surviving solely because of bronies at this point
The ratings for MLP apparently lean towards bronies, who contribute a lot towards making it pretty much the #2 show on the Hub, just behind Transformers, but the entire network leans heavy towards the male demographic, so it's not-entirely-surprising that even MLP gets more male viewers, and the show's success outside of little girls is seen as a welcome support for their plan to reach out more to the little girls demographic. Hasbro
wants little girls to tune in, so if they can keep putting out triple-A shows while they wait for this audience to materialize, and there's no penalty for that kind of investment, then they know that they are absolutely on the right track.
But toy sales apparently come mostly from little girls, and they have recently pushed MLP into the #1 position in Hasbro, outselling Transformers, which is currently suffering from a wonderful lack of terrible Michael Bay movies. Don't cry for Transformers though, because they have a new terrible Michael Bay movie coming in 2014 starring Marky Mark instead of Shia the Beef. (Edit: I take back my cheerful sarcasm. Weep for them.)
Toy sales can keep a toy show on the air even if it has bad ratings.
So bronies are great news for Hasbro, because we turned what was apparently MLP's only current weakness into a strength, but we're ultimately not needed as part of the game plan.