Except that this isn't entirely accurate. See, at the peak of its half-season run (assuming half a season can be said to have a peak), Firefly was pulling in more viewers per episode than the concurrent seasons of Buffy or Angel.
I might be mixing up my Farscape/Firefly cancellation information, but didn't Firefly cost a whole lot more than Buffy or Angel ever did per episode?
Regardless, yeah -- a new show on Fox is, generally speaking, going to have higher ratings than a new show, or even a continuing show, on UPN or WB. That's just a matter of being one of the big four. I'm sure that Firefly also did better than a rerun of Alien Resurrection on TBS airing at the same time, but that doesn't make Firefly a success.
The problem isn't that Firefly wasn't a success. The problem is that Firefly wasn't a success by Fox's standards. If the show had been on UPN or WB, we'd probably still be watching it.
I agree with everything but the first sentence of this quote completely. I think that the first-sentence is a non-statement. You can judge "success" in a whole lot of ways, but the only one that's going to keep you on a network is whether or not you're a success by the standards of that network.