It's weird, though...Fox seems to have a habit of cancelling things right when people are starting to get an interest in it. To wit:
Family Guy: Swapped around on a bunch of different nights, cancelled, DVD sales go through the roof, return to Seth McFarlane on their knees begging him to come back.
Firefly: Not one I watched, but saw Serenity and thought it was decent. Fans have been clamoring for this to come back and, despite the DVD sales, Fox seemed like they'd rather fart in a dumpster, let it fester for a few weeks, then dive headfirst into it than renew this show. Yet, despite the fact that Dollhouse, good or not, is one of Joss Whedon's weaker ideas, they don't seem keen in putting THAT on the chopping block.
But at the same time, Fox will sometimes let some pretty awful nonsense stay on well past its due date as well. "The War at Home?" The REALLY poor man's "Married with Children?" That lasted two seasons.
I think what the cable companies need to start doing is having Nielsen-type chips implanted in cable boxes that allow (voluntary) enrollment in a ratings demographic, so that if you DVR a show or tune in actively, it sends a ratings hit to the company. I think the demographics would change considerably if they started doing that. I know people that were upset that "The Unit" got the boot, too, which fought (and won) to stay on the air for an extra season.