With Family Guy, I remember watching the first episode and laughing my ass off, then never watching it again. With AD, I'd never seen it in an original broadcast... For me, I'm not a regular television viewer. Which is why tivo is so great, because I tape the 1.5 shows a week I actually try and follow, and could care less about the rest.
Just a theory, but I think peoples' short attention span and busy schedules are what have killed good tv the most. Hell, even 30 Rock (as of last season) was struggling for viewers. Glad they kept it going. When was the last time you worked your schedule around 'must see TV'?
The writing of AD amazes me because they clearly wrote in extremely subtle jokes and references (even in the first few episodes) that manifest themselves much later in the series.
"I was the world's first analyst and therapist!"
"Yeah, and those business cards almost got you arrested."