It starts with the Pilot for Alias (known as "Truth Be Told"), which also has a firm beginning, middle and end. Running 66min, it was directed as a stand alone movie so that if the series wasn't picked up they could release it on DVD. His other pilots were only 42minutes, but not Alias or Lost (which was filmed together as 1 movie, totaling 82min.)
Yes, Lost is much more open-ended, but so is Fellowship of the Ring. It establishes drama, character and conflict better than most theatrical features.
I personally agree about Joss Whedon's extraordinary television work, but I also agree that it's a grey area, because they're not feature length and require knowledge of what's come before and after. Like I said, these decisions should be on a case by case basis and in the case of J.J. Abrams, Alias:Truth Be Told and Lost:Pilot deserve to be part of the poll.