Importance of a good pilot

Lately I have been watching a lot of tv shows online, mostly marathon style. It occurs to me that a lot of pretty good shows don't last very long and in fact are canceled well before they last a year.
Two that jump to my mind are Wonderfalls and Jpod.
Wonderfalls is a show about a young woman, Jaye Tyler, who is 24, Ivy League School educated who moves back to her hometown, Niagara Falls, NY, lives in a trailer and works as a retail clerk in a gift shop near the falls.
While Wonderfalls developed into a pretty good show, (I've watched five so far and it keeps getting better) the pilot was at best ok and could have lost a lot of viewers. It seemed to lack direction, some of the characters were obviously miscast, and it relied on the premise (which was that the main character, Jaye Tyler, can hear toy animals speak to her and give her advice and direction in life) to carry the show. The main character is played by Caroline Dhavernas, who is fantastic and is worth watching even on a bad show, which this is not. But its not enough for most viewers, who might have abandoned this show 3/4 the way through the pilot. The writing is witty and fantastic, but there are too many characters and too many stories for a pilot.
As the show progresses, it settles in nicely and tells a different episodic story each week, builds on Ms. Dhavernas acting and minimizes the poorly cast characters of the sister, brother and bartender/boyfriend. The writing is fantastic and keeps you interested, but alas, most viewers were probably long gone by then.
It points out a valuable lesson. Even if you have a great premise, a young talented star actor, witty writing and some interesting supporting cast members, if the pilot doesnt deliver, the viewers will be gone by the time it gets good enough to keep and build an audience.
In this day and age, with all the money that is at stake to produce ratings, you cant get away with a show that finds itself later. The pilot must sell the show or it will die.