I don't like that rule. Sure, it sucks when a show you love gets cancelled, but I'd rather have a little bit of something awesome than nothing.
Great example, Studio 60 on the Sunset Strip, a 2005 comedy show written by Aaron Sorkin. It's ratings weren't great and it was canned, but I think it's amazing, and I rewatch that one season at least once a year.
I agree, Studio 60 was awesome (I don't follow their rule). But at the same time, I feel very unsatisfied that I got so little of the story arc with the cancellation.
S60 really got worse as the season went along, not helped by Amanda Peet getting pregnant and needing that storyline to be written into the show. I'm not actually sure how much of that was based on "shit we're not getting a second season, how do we tie up as many loose ends as possible" and how much was just... bad (relatively) TV.
Either way, while I agree with you on not liking the ending (and would have loved it to become as popular and long-running as The West Wing), still extremely glad that it became one of my "re-watch whenever I have nothing else to watch" shows, and still love it each and every time I see it.
Also Sports Night from the turn of the century, two seasons of fantastic writing and amazing characters. Check it out if you haven't seen it - although I do have a friend who's also a big Sorkin fan, and loves WW and S60, but didn't particularly like Sports Night, so perhaps it's not as good... but it was the first TV I saw from Sorkin, and I still absolutely love it.
Great example, Studio 60 on the Sunset Strip, a 2005 comedy show written by Aaron Sorkin. It's ratings weren't great and it was canned, but I think it's amazing, and I rewatch that one season at least once a year.